we have a monopoly pretty much everywhere for Internet services

Fortunately, that's not true everywhere, and municipal fiber is becoming more and more common.

5G home internet

The problem here is latency. It's entirely sufficient for most web browsing and video streaming use-cases, but it sucks for multiplayer gaming and other interactive use-cases (e.g. video calls). So while it's probably a solution for a lot of people, it's not really a replacement for physical cables.