That sounds like the developer's problem, not the browser's problem.
I mean, I could half-ass my work a lot more often if they'd get rid of these burdensome restrictions on cross-origin requests. But they ain't going to.
Domains are never going to be just one origin. If we could force developers (or, more precisely, ops teams) to do this, then CORS would never have needed to exist in the first place, because there would be no need to allow any crossing of origins in the first place.
But, at every point in the web’s evolution (including today), there was always been something that needed to live on a different host or port for some reason or another—usually because it’s too leading-edge for load-balancers to understand how to route it correctly.
TCP load balancers that can handle long-lived flows with connection stickiness et al, are a very modern invention in the web’s history; and even they still stumble when it comes to e.g. WebRTC’s UDP packets, or QUIC.
