The problem is fluctuations of the load on the tower and random signal outages which can happen at any time. Also in my experience LTE links sometimes drops when working for long periods on it, meaning I need to reconnect VPN and do other annoying actions.

And that's not even starting on the problem of coverage. Especially in the apartment blocks with a lot of rebar in the walls. And 5G higher frequencies have even worse coverage that 4G. If I have a problem with Wifi inside my home I simply buy repeaters or wire a new AP with a cable. WIth cell network I can't do this.

We are a long way from using cell network as a primary one (if alternative is available of course).