And for comparison, they are still separate in OS 4.x, even though lots of other stuff has been done to Workbench.
So probably for a good reason ...
Best regards,
Niels
RAWBInfo I think is because it needs ReAction, which isn't guaranteed to be available if you've booted a barebones WB installation (the built-in info window uses gadtools, which is always available)
ASyncWB I guess is separate because it is easier to have a program which patches the OS and is already a separate process, than trying to make WB spawn a new process internally when copy operations are initiated (also it probably uses ReAction again? Although there's no reason why such a simple UI would need it)