The private market made the exact same choice in the 90s, but instead of just being something that cost maybe more tax money than it should, it was hyped up and full of lies and marketing and bullshit and burned tons of cash for really stupid projects and caused a serious recession.
So..... not really a point for privatization here.
The 90s were dominated by modems and around the turn of the millennium DSL connections. Fiber internet (to the home) didn't start until much later. The backbone was getting fiber deployed before then, but there was never some kind of unusual bandwidth crunch in the UK. The private sector managed the rollout just fine.
So..... not really a point for privatization here.