I frankly doubt they thought about such practices.But as we know anyone can assemble an arbitrary circuit(s) using multi way adaptors and fan heaters or whatever and the other option is to make sure all multi way adaptor flexes have 4mm2 cable etc etc, a fused plug is more economical.
A simpler version of what you have said, not invoking multiway adaptors, is that if we did not have fused plugs, then every appliance/equipment capable of producing an overload would presumably have to have a flex of at least 4mm² if it might be plugged into a 32A circuit.
Even worse, although I may be wrong, I'm not convinced that the regs actually preclude the possibility of, say, a 45A sockets radial circuit (wired in 6mm²), or even more than 45A - and if that is theoretically possible, then goodness knows how big and impractical appliance flex would have to be to be guaranteed to be OK in any installation if there were no plug fuses!
Kind Regards, John