1. They walked here.
2. They walked away.
3a. Who says there are no remains?
3b. Animals ate them.
3c. 200,000 years is a damned long time. The remains could simply have dissolved.
Anyway, if these were nomadic hunter/getherers you wouldn't expect to see much. Heck, there's not much physical evidence of such tribes that existed a few hundred years ago.
Yup. There are graves in this area (Mobile) from the mid-1800's and there is absolutely nothing left in the ground underneath the grave stones. The soil here is very acidic and everything underground is 'eaten' away.
Yet some of these fossil and rusty tool worshipping 'scientists', who will divine cultural histories and write entire volumes from the discovery of a few tools or bones often discredit the miracles of Jesus Christ as 'myth' or 'superstition', even though four detailed books of the accounts are written by His disciples and learned contemporaries, as well as endless other ancient commentaries by men who knew Christ's contemporaries and disciples, and by men who knew them, and so on.
Early Hominid and Homo remains (fossils) are plentiful around the world.
There is no theory that any Homos originated in No America. Walking here is no mean feat (no pun indended). Walking away is just as difficult.
Still, an interesting idea that we had our own primitive types in So Cal 135,000 years ago. Some might even say they never left, and now run the CA state government.