Think about it! The rear sprocket is inside the drop outs and so inside the frame - the chainwheel is outside the frame. You need to be able to split the chain somehow to fit it unless you have a removable rear subframe. Some 'full sus' mountain bikes may accommodate this, but a normal one piece bike frame (rigid rear) definitely doesn't.Huhh why need to split frame ? Just replace chain cogs with ones for belts an fits just like a chain.
It's similar on a motorbike - to fit a non-splittable chain means you have to remove the swing arm. A real pain. Been there, done that. A drive belt is manufactured as a complete ring and that's what you're stuck with.
Rog.