I've noticed this too, as I had hoped to skip the building process and buy an insta-coop. We ended up buying a shed kit and outfitting it for chickens to get the space I wanted. Builders have to be aware of moving it... so many are small and capacity is over rated. To get something that will house 8 chickens through bad weather without a covered run, you'd basically need to hire a shed hauler for transport. Built on a skid helps too for transport. So a lot of them are like 4x4 or 4x6, something that can get into a truck bed. Hard to sell things that aren't easily moved.
I've even seen open air rabbit hutches sold as chicken coops, and with this being zone 3 with legit winter, that's a terrible idea, for chickens and rabbits.
Some were designed in the strangest ways too... hard to clean, bad access, not enough floor space, just generally not efficient at all and $500 on top of it! The shed kit we got was $280 and an 8x10. Just swapped the doors and cut some window holes out, and did a better floor covered with linoleum. Outfitted an x shaped roost, and some stackable totes as nesting boxes. Built a 10x10 covered run attached to it, and then fenced a buffer area around it and the compost area, for minimal free range and turning of the compost, then I have the choice to let them into the whole yard or not. So they get a total area of about 16x50-ish. Our yard out back is 50x120, so they don't get full time yard access. Too much free time would have them eyeballing the 4 ft fence around the yard for escape.
But yes, there are enough bad coop designs out there to scam a beginner that isn't sure what they're looking for. I've seen some home built jobs too that are dark, lacking air flow, and built from unpainted particle board on top of it!
