One way councils can force the issue is to deny planning permission unless builders can show they've engaged a telecoms company (doesn't have to be BT, could be Virgin or Gigaclear or Cityfibre). After all, we don't accept houses built without electricity and water. Why should we accept houses with subpar connectivity?

I recently got a new fibre connection (not from Virgin or BT) in my newish flat and I was taking to the chap who installed it about exactly this. He told me that it's actually the builders who pay BT and Virgin to come and connect up their buildings. This is so they can then market them as being almost "plug-and-play" with these services as some buyers look for this. The other smaller providers can then come along and install/connect their stuff but at their expense, and as you say, often afterwards. He said that this is made harder since installing afterwards means dealing with managing agents (in the case of of a block of flats) and this can be painful, which I can 100% believe. Perhaps the situation varies depending on where you are in the country, this was London (where there are no £350k houses!).

One of my friends parents a couple of decades ago brought an architect designed house and the designers/contractors neglected to put in any ducting!

Took them ages to get POTS - You can see why Civil engineers make Architect jokes