Why opensea (Wyvern) are using proxy registry?

From what I see when someone try to sell something on Opensea this is the process:

  1. The user creates a proxy registry for his token.
  2. The user approve the proxy registry to access his token.
  3. The user listing his item and sign a message to allow the buyer to buy later using that signed message.

Now my question is: Why do we neeed the proxy registry? What exactly it gives that cannot be done without it?

I have tried to read the Wyven whitepaper, source code, Opensea help center and all the docs, all the blogs posts published by both org's, and didn't find an answer.