Why does SNI even exist

Whoever designed TLS did not expect third parties, so-called "content delivery networks", "cloud providers", etc., wanting to offer hosting to an unlimited number of customers ($$) on a limited pool of IP addresses

Problem of cleartext SNI was solved in 2011, well before "QUIC" existed

http://curvecp.org/addressing.html

Without TLS and without SNI anyone can host multiple HTTPS sites on a single IP address