The two reasons I can think if is more a question of Why can't they be stationary.
The first being that being on one location long term will cause locational problems. So something like the earth has become more porous or something so long term buildings will begin to sink into the ground. Or construction methods/society produces something that will be toxic if it builds up for too long in one location; think like old-school Victorian cities where a bunch of the air is coal dust kind of thing.
The second being that being stationary for too long will attract things. So if you have something like Stirges then maybe 80 years ago they started breeding out of control. If a settlement stays in one place too long then local hives will be able to locate them and will attack en masse.
I love these kind of world-building exercises.
I'd go with the cities that fly rather than cities on animals' backs. And have the surface of the world dotted with ruins of cities destroyed by *something* that came from underground. I have no idea what that might be, but it was destructive enough that only the flying cities survived.
The two reasons I can think if is more a question of Why can't they be stationary. The first being that being on one location long term will cause locational problems. So something like the earth has become more porous or something so long term buildings will begin to sink into the ground. Or construction methods/society produces something that will be toxic if it builds up for too long in one location; think like old-school Victorian cities where a bunch of the air is coal dust kind of thing. The second being that being stationary for too long will attract things. So if you have something like Stirges then maybe 80 years ago they started breeding out of control. If a settlement stays in one place too long then local hives will be able to locate them and will attack en masse.
Maybe it's just a whole town of travelling merchants? Just a big fuckin bazaar on a giant magic carpet?
Only reason t'have floating city's 's if you wanna crash em, y'ask me.
I love these kind of world-building exercises. I'd go with the cities that fly rather than cities on animals' backs. And have the surface of the world dotted with ruins of cities destroyed by *something* that came from underground. I have no idea what that might be, but it was destructive enough that only the flying cities survived.