actually it's not. I've had a few species that just go into stress curls in oversized cages. Putting them in smaller cages and they're happy as T's can be. Both of my A. seemanni have done this and my G. pulchra.Cage size is a myth.
Smaller cages make it easier to get their prey also, depending on what feeders you're using. My boehmei is lazy and likes to ambush as the prey run by, same with a number of my other T's, they won't go hunting for it like the GBB, genic, and Lasidora species i have.