God these things are horrible. They're huge, they can't fold away, and they require fuses. And the receptacles all must have switches, and must be exactly the same.
Leave it to the British to shoot themselves in the foot for no reason. Why not Schuko / Europlug? Because we have to have our own standard that's worse, that's why.
Switches are not compulsory, they're just conventional. MK, for example, will happily sell you unswitched sockets (and without the "not to standard in the UK" warning for some of their other products).
Also not sure what you mean by "exactly the same". You can get single/double/triple in a variety of designs and colours. It's a socket - how much variation do you need?
"A variety of designs and colors"
I only see a very few actually available, even via the internet (when I've looked). But you're probably right. I lived in the U.S. for a while, where variety in receptacles is easily obtainable.
Rather, I think the British decided to iterate (for better and for worse) on their earlier design that looks a lot like BS 1363.
Personally, having lived for an extensive amount of time in places with Schuko ("Europe"), NEMA ("US"), and BS 1363 ("British") plugs/sockets, I will take Schuko any day over the other two. Schuko stays in place, is grounded when it needs to be, is flexible when it comes to how it leads the cord out of the plug/socket, and so on. For all the touting of safety, "no sparks", etc. that we hear about BS 1363, I have never seen it out of a Schuko (NEMAs on the other hand...). Yes, BS 1363 improves upon NEMA, but that is a very low bar.
Leave it to the British to shoot themselves in the foot for no reason. Why not Schuko / Europlug? Because we have to have our own standard that's worse, that's why.