In my experience, nothing.What exactly stops people from playing other games or creating other games currently?
Over the past six-odd years I've played (as best I recall) about 3 sessions of AD&D, one session of Moldvay Basic, and 5 or 6 of 4e D&D. (And no 5e D&D.)
In the same period I've played over twenty sessions of Classic Traveller, close to that of Prince Valiant, more than half-a-dozen of Cortex+ Heroic Fantasy (Vikings, MERP/LotR), a similar number of sessions each of Burning Wheel and Torchbearer 2e, several sessions of Agon 2e, and a variety of one-shots (Cthulhu Dark, Wuthering Heights, The Green Knight, In A Wicked Age).
The only obstacle to playing more non-D&D RPGs, in my case, is being able to coordinate available time with my friends I play with.