So I'm working on a world where 19th century humans discovered a portal to a faraway alien planet, and since it's the 19th century they decide to colonize it.
Just few decades after the discovery there is already a fairly big colony, with roughly 7 million people in it, mostly concentrated around a single big city, with the economy based on extracting and processing the very abundant resources of this planet.
But the problem is, why would people even want to migrate there in the first place?
The living conditions on this planet are absolutely miserable. There's next to no sunlight, the climate is cold, and the city itself is an industrial-mining town suffering from a serious pollution problem. The alien fauna is not exactly friendly to the settlers either. There's all the good stuff, small pests that love to eat any food, clothes or furniture they find, medium sized wild animals that harass the outskirts of the city, and giant monsters that usually manage to destroy a neighborhood or two before the military deals with them. And since these humans are the only intelligent species on the planet there's a lot of these dangerous alien animals running around. Not to mention the more supernatural-alien phenomena that haunt the city every now and then, like the zombie-like plague that appears in the slums every so often, or the alien artifacts that cause humans who find them to go insane. And the food made from plants grown there can be described as barely tolerable at best.
Since most of the populated parts of the colony are located far away from the portal itself, the travel and even contact between the Earth and the alien world are very limited. It takes around one month to travel from the main city back to Earth, and another month to return. So any aid from the homeland, military or economical, takes a while to arrive. And this isolation from central authority made it a heaven for radical elements, so the unrest is high.
Overall there's nothing that the human settlers can't deal with, but it's by no means a nice place to live in, even now. And during the early days it was even worse, since people didn't know much about the dangers of this world.
The government wants this colony to succeed since it provides an incredible amount of valuable resources, like precious metals, coal, oil and rare earth elements. And there is an added bonus in the form of mysterious alien artifacts. But what would attract people to live there over any other place on Earth? For a regular person, life there would be just like living in any other poor overcrowded city on Earth, but with the added cons mentioned above. Why migrate to that place in particular?