I also believe that it’s mostly an architect thing in the larger homes. They apparently don’t like the look of our receptacle outlets in the walls. I guess I do kind of like the look of them being installed horizontally in the baseboards, but I also think it’s a pain to have to always squat down on bended knee every time you want to plug something in. I’m going to assume that in situations like these, hired help will likely be doing most of the bending and squatting for the homeowners anyway.
As bad as it seems for installing electrical outlets, I think it would an even bigger pain installing central vac hose type inlets and aligning the associated piping and wiring within the baseboard.

I always operate under the premise that the less contact other trades have with my wiring, the better off things are. I’ve had ham-handed carpenters take it upon themselves to cut in the baseboard receptacles before, without consulting me first, and they were a disaster. Undersized metal boxes they picked up at the hardware store, holes cut so big the ears were just floating so the screws wouldn’t hit wood, NM behind the boxes in the wall pinched and folded like pipe cleaner, NM sheathing ripped and damaged conductor insulation. It basically turned into even more of a pain for me, because I had to first undue the damaged they did before I could begin to make things right.