Well, they do? Sodium, for instance. It's a mod, not a full rewrite, rewriting the client from scratch would mean a lot of boring work like speaking with Mojang

Well, they do? Sodium, for instance. It's a mod, not a full rewrite, rewriting the client from scratch would mean a lot of boring work like speaking with Mojang's server, but I understand Sodium basically rips out and replaces the entire graphics pipeline of the client.