First, planets created through natural processes are nearly guaranteed to have some degree of axial tilt, which is the primary contributor to seasonal changes in exposure to parent starlight (herein "sunlight", even though it's not!).
Now, you're asking why an artificial planet would have seasons (in particular, why its artificial construct inhabitants would want seasons). I can think of two main reasons:
1. Engineering tolerance
Your machines end up not caring about axial tilt because they simply don't care about seasonal fluctuations in temperature and sunlight. Being machines, they can tolerate these fluctuations without any operational impairment, so they don't care.
Put another way, they want the cheapest option, so they "want" seasons by proxy: it may end up using more energy, more time, or more complicated processes to create a planet with a near-zero axial tilt, so they just go with the cheaper option that results in an axial tilt somewhere between -20 and +20 degrees, for example.
Even though your artificial life forms are, well, artificial, that doesn't preclude them from seeding and farming natural life. Perhaps they plant varied bio-fuel crops as an efficient source of hydrocarbons to fuel some of their processes, and those crops function better with growing seasons and off-seasons. Perhaps they farm some kind of migratory animal that needs to be migrated between grazing lands so they don't eat all the grass, and seasons are a free, sustainable way to do that.
The only minor hitch for this option is that your "inert gases" in the atmosphere might not be conducive to crop growth. Most Earth crops rely on carbon dioxide, at least (that's where the carbon comes from). There are other potential reactions, of course, but that's probably a bit beyond the scope of this question.