Had a longer answer that went away for some reason 😭

Your criticism is fair, but:

• Using the email as a seed on the generator goes halfway there, here’s an example, although of course it could never change
• Centralizing the avatar opens that service up to be grabbed for tracking like Gravatar did, or breaking the security of a site by injecting code without the consent of the site owner. The usual tradeoff between security/privacy and convenience.

Would be good to have a good user-managed way to do the same (well, beyond using an image on your own hosting, i guess)