The three phase is what kills interest in it. You just won't see a three phase installation anywhere in the UK where the demand is for less than ~125A single phase.
This is simply bloody stoopid. But, as you wrote, it's a fact of how it's always been done, so that's how it is being done.
Single-phase anecdote:
Once, I worked with TV. Analog TV, at a production company / OB vehicle supplier. We did a job where the contribution link (the way home for the TV program) was a BT satellite feed. Our OB van, which was the center of mains distribution as well, had a 63A three-phase input, and the venue, being in continental Europe, had supplied exactly that. The mains outlets for technical power were a bunch of Schukos, some 16A single-phase blue MK Commandos, and a couple sizes of three-phase outlets, IIRC 2 off 16A and 1off 32A.
The uplink van had a 32A MK Commando single-phase blue inlet..
![Face Palm :palm:](https://www.eevblog.com/forum/Smileys/default/xfacepalm.gif.pagespeed.ic.EBDwh1hCfo.png)
Took a lot of swearing and cable bodging before a suitable feeder cable could be arranged.
A sensible vehicle woulda had a 16A three-phase inlet; it is immensely more common, and carries 40% more power than a single-phase 32A -- which usually is fused 25A anyway.
Oh, and now I work with TV. Again. This time, we're filling a lot less racks, but every bit of kit that goes in draws more watts than the old stuff, so that we're down to half the cabinets and double the power.. Progress!