Games, audio/video calls, screen sharing - any peer-to-peer traffic is a royal pain in the back with NAT and CGNAT especially.

Larger providers (zoom, apple/facetime, twitch, ...) just set up relay servers and avoid p2p altogether - which cost money, increase latency/jitter, and decrease privacy. You can argue all of that are hidden costs of sticking to IPv4 for longer than we should have.