I don't think the OP is talking about orbital habitats, what they're talking about is space resources found by surveying with science ships, and adding food production to the list of things you can get from mining outposts.
I could see a lot of explanations for this game mechanic. You might find minerals that are essential to farming like phosphorous in an asteroid belt, or you might find an easily accessible food source on a planet that has a biosphere. It could simply be in a good spot for free, natural sunlight ideal for growing plants, so what you're essentially doing is building an orbital hydroponic farm without a starbase.
From a game mechanic perspective I don't see a problem with it, unless you're playing a synthetic empire or otherwise don't care about food and you don't want your sector governors building food mining stations. But even then, you could just trade it away to other empires so it's not a total waste.