Indeed. Anybody but the biggies will have an impossible task trying to convince people to verify their ID, so all the smaller sites will switch to only allowing registration/sign-in through Google/Apple/MS's Oauth, and depreciate the username/password option. When "signing in with Google/whatever", Google will simply pass a flag "adult" along with authorizing. In the end, they become the gatekeepers for the whole web, collecting tremendous valuable data in the process and gaining even more power over your identity.

Always keep in mind that the small players will always take the easiest option, and the big players want more control.