You are correct with this comment yea, the biggest drawback (which as acknowledged we have seen on lemmy) is the anonymous of the account. It's easy to spin up spam instances, and due to how federation works its hard to combat against it. I remember LW had an issue regarding that a bit ago with someone threatening to just keep changing domains to avoid blocking, which is indeed a problem for any of these style services. I agree at large scale, most sites are not going to want to have to put up with losing that level of control moderation side. It creates a lot of headaches and for most sites it's just easier to enforce a policy that forces disclosing PII.