The only valid (but not raised yet) argument is that something like this could endorse nostr and I don't believe they want to do that.

Protocol or not, there is not enough surface area of products that have reached mainstream for it to be considered a useful protocol that should be incorporated.

It's like deciding to integrate a remote file sharing protocol when there are 3 others to choose from and so you'd wait for it to become 1 or for at least one of them to become dominant before integrating.