> I know they have team(s) of very smart people dedicated to solving this issue (at least at the individual level).

Do you actually know, or are you being generous and still trying to assume good faith from a company that disproved it several times?

I don't see a business reason for them to take action. The spam comments don't open them to any legal liability (they already get away with much worse), YouTube has a monopoly so no amounts of spam will drive users away, the spam contributes to engagement numbers and the advertisers don't seem to mind.