That is one reason.

Many people aren't even aware of such draconian policies they are signing up for. And companies are probably counting on it too.

It is also possible that even the owners of the company (especially small, family owned companies) aren't aware of these dumb policies. They just trust their lawyers to write up the contracts. There was a comment recently on HN - employee reads up the contract, goes to the owner to ask about some clause, and the owner himself is surprised and calls the lawyer to sort it out.

Big companies that spend shit ton of money on lawyers have no excuse - they're likely doing all this intentionally.

It’s like they select a box for “maximum liability protection” not realizing some of it provides no protection at all

I had one success simply not signing a non-compete I was handed on orientation day. I returned the packet of docs without that one and never heard a thing about it.

My understanding (from working with lawyers in the past) is that it is enforceable in some states and unenforceable in others. I'm not a lawyer, though, and so don't really know first-hand.