This is a big reason why most modern Western large-scale infrastructure projects get delayed and cost overruns. People making decisions treat construction as if it was cloud computing: just pay for how much you need, when you need it. Some sectors are highly specialized and if their future use is not predictable, they must charge a high premium for that uncertainty.

Basically they are acting like the sort of third world country that does grandiose vanity projects.

Having lived in one that went through a phase of that (Sri Lanka) it strikes me that this is yet another way in which the UK is becoming more like Sri Lanka (all bad ways - not the things that are good about the latter). I see it in education too, for example.