Maybe I’m just clumsy but I did it multiple times as a kid. There were never enough sockets (I helped my dad install a bunch when that was still legal in the 80s and 90s) and sometimes you move an appliance from room to room, like a hoover.
It’s really not that complicated and I’d feel completely comfortable doing it myself today but I understand how that may not be true for everyone so the requirement is probably reasonable.
That said, you're theoretically supposed to do a full set of earth resistance measurements etc. on the new wiring, which is hard if not impossible unless you've got proper electrician's test equipment. But in reality no one does that when DIYing it.