So, it's the future and society has long since became divided upon distinct lines of rich and poor. The rich upper-class living a life of luxury and the poor lower-classes living each day at a time, thousands of meters above the Earth in the sky, in massive balloons and the tops of skyscrapers, the ground reserved for the rich, but why?
For what reason could the rich possibly have to want to live on the ground as opposed to the sky up above?
In the Foundation series, Trantor (a planet-sized city) has one patch of green on the entire surface; the emperor's palace. Here, similarly, the only greenery is surrounding the mansions of the rich. They are the only ones able to buy land, and then not put a tower on it. This is an act of conspicuous consumption, and does not need to be purely logical.
Until not too long ago, the higher floors of a mansion were the places where the lowest of the servants would have their quarters: cold in winter and hot in summer, humid and real mouse traps in case of a fire, for no reason the owner of the house (and consequently a rich man) would have settled right there.
You can use the same reasons in your case:
To live longer.
To paraphrase from a book by Alan Lightman, ‘Einstein’s Dreams’
To slow the passage of time, and live longer lives than others, the wealthy lived deep in the gravity well and the poor lived high atop the mountains and in orbit around the planet where time passed faster. The amount of difference in the relative length of life was barely seconds but it was the idea of it, of losing even a moment of life to forces outside their control, that resulted in the practice.
Alternate Answer:
For same reason, people wanting to live longer. But it was because the air was polluted by particulate matter that slowly poisoned the inhaler. The city where this was the practice, of living as close to the ground as possible, the flora helped cleansed the particulates and the shape of the valley -- similar to Denver -- caused steady airflows that kept the air near the surface fresh.
But higher up, the brown cloud of particulate poison hangs over the city -- like Denver and its famous brown cloud -- trapped by a seemingly near-constant inversion layer. Some days, in winter, the temperature inversion clears and the particulates are blown out of the valley, but it starts accumulating again.
Now, in the future, they built giant domes and processed the air, removing the danger, but the status of living close to the ground, demonstrating one's virtuousness and prosperity, is deeply embedded in the society.
They use strange sounding phrases like 'may you sleep in the mud' 'dirty shoes -- as tidings of encouragement and celebration.
Space. (In the room to live sense, not the place located above the atmosphere.) Why have so many rich people throughout history maintained lavish country estates? You have room to make your flower gardens, ride your horses, or do all sorts of other things. And since you've relegated the poor* to living above ground, you have lots more room to do these things.
*But this is perhaps not the wisest of choices. See e.g. Navarth: "Castles in the Clouds and the Anxieties of Those Who Live Directly Below by Reason of Falling Objects and Wastes" :-)
A potentially very simple answer for this is the just the fact they are wealthy. Depending on population levels and their spread, living planet side would be quite the luxury.
To give a crude explanation, we can just look at Earth as is and deem it 1 Earth of living space based on surface area - a dull measurement but it lets us ignore the question of building on ocean floor vs just somehow paving over entire oceans. Now we just look at an estimated amount of iron on Earth - about 300 million cubic kilometers. Turn that into space stations and even accounting for some loss by saying you want steel instead of iron and you'll have roughly 1 million Earth's worth of living space.
In addition, just talking of Earth specifically, one can take historical value into property prices - after all it's homeworld and is bound to have more than a little history and sentiment inflating that living space value.
Certainly one can go "yeah but Im rich enough to own a large asteroid on my own"... congratulations there's easily millions of those depending on what you call "large"...meanwhile the truly wealthy own swaths of the homeworld which has a very finite supply since you can't just "tow in" another Earth
Perhaps the skyscrapers were hastily (and unsafely built), and are cramped and crowded. And the balloons are not as airworthy as they the powers that be claim they are. Living on the ground means not having your building collapse or your blimp city fall from the sky.
Where I live, the poor are in ugly concrete high-rise blocks (hello Grenfell Tower*) the rich have nice houses with gardens.
It has always been thus. Even in Roman times the urban poor lived in cramped accommodation in tall buildings ('insula') while the rich lived at ground level villas with trees, fountains and plenty of space, and easy access to amenities. Weekend cottages, rural villas, a place in the country, a hunting lodge, a place on the beach, a little getaway by the lake or in the mountains: all of these are for the rich folk and the effect is completely spoiled if you make them 50 storeys high.
The best a tall building can do is give the illusion of the spaciousness and convenience of living at ground level.
Parks and Greenery.
In a high-rise building or even some appartment blocks floating around in the sky, there is no feasible way to have large parks.
The rich, on the other hand, buy up acres over acres and enjoy the lush vegetation around them, whereas, the poor sit in their floating flats and the only thing they see is clouds. Clouds over clouds.
For buildings: if they're tall enough, the upper floors will be a pain to get in/out of: the more floors you've got, the higher a percentage of the ground floor needs to be made of elevators to adequately service the upper floors. The point at which this becomes a problem is tall, but not absurdly so (we're starting to bump up against the limit with the tallest buildings in the world today). If you just ignored that and build stupidly tall buildings with inadequate elevators, you'd end up with the upper floors being a pain to get in/out of.
In the near future, the push to green technology to keep the planet alive, to be pollution free, to pull back rising heat and sea levels, we delegated living to the tops of huge sky scrapers above, all structures for general manufacture were to go to the sky, a place, high up enough that support balloons (doubling as storage units for the methane/gas used to power several systems) would reduce the need for the massive strength of columns and skyscrapers of the past to hold up the ring, The ring even as a thin 50km wide band, was able to house the world, so the earth could be free to replenish and regrow after the devastation we wrought upon it.
In Time, the surface became home on to those who could afford to transport goods back down to the surface. A ticket to the surface, a holiday trip, was the price of a years salary for the bulk of the population, so only those in power, and wealth would or could live on the surface, while the spacers mined the asteroids, and brought back materials to the ring.
Food, Oxygen, and other necessary things to survive
The rich would wanted to have an easy way to get their needs fulfilled. All sources of food (plant and animal based) are located in the grounds. Oxygen is sparse on high places. Other materials also found on ground (gold, silver, etc)
We are land creature, thus the ground will always be our best bet to survive.
They can and will do whatever it takes to take the land, and put other poor lower-classes to live on skyscrapers, why? So that they can take everything, and become richer
