Sure, and that's a problem. However, here we are talking about finance, not value transfer which is a lower layer. For value transfer, like money, identity is not required (even avoided ideally).
Back to the initial point, that's why address reuse makes sense in Bitcoin.
But when talking about a messaging platform or protocol, identity becomes relevant because you might need to know who sent the message, or you might even want others to know you sent the message. And reputation is another thing to consider. All pointing to identity.
These days even lower layers are KYCed. Venmo, cash app, apple pay, they all have your ID. The only thing that doesn't use your id is pure cash, which virtually no one uses anymore.
