I think the problem is people are lazy.
With interior maps people literally just loaded that stuff up and explored it.
I know this because me and a full server spent hours exploring interior maps.
But now people have to make their own maps (also learning how to make a gamemode is hard as stuff) no one has time to build their own map.
With that being said I would gladly make a gamemode of my toystore build with public brick building on so people can build in it like a normal interior map but I just can't figure out how to make a gamemode. It's too complicated.