* YouTube has no liability for incorrect take-downs (17 USC § 512 (g) (1))
* That limitation on liability only exists if they restore access to the disabled material within 10-14 business days of receipt of a counter-notice (17 USC § 512 (g) (2) (C))
https://www.law.cornell.edu/uscode/text/17/512
YouTube doesn't have to host any content they don't want to. However, it seems likely that a court would say "that doesn't absolve you of complying with the counter notice provisions of the DMCA. You can't just say that you don't want to host any content that goes through a counter notice." There are always limitations on the whole "we don't have to host things we don't want to." I doubt a court would let them use that as an excuse to ignore an explicit mandate of the DMCA, but IANAL.
I think the problem is more likely that creators don't want to sue YouTube or have the resources to go up against Google.
Why not? (at least legally speaking, it'd be a PR disaster I'm sure)
YouTube is not obligated to host any videos on their platform and US law allows for businesses to discriminate for almost any reason (except specific protected classes like race or sex).
DMCA has protection for creators. You can say "Copyright holder is wrong, put my content back up and I'll see them in court." and "They did this maliciously, I'll see them in court."
However, YouTube fake DMCA system is using the provision of "We don't have to host any content we don't want to." so creators are stuck dealing with corporate bureaucracy. Personally, I think YouTube should lose DMCA protection if they want to run this side system.