I seem to recall some theory about how the speed 33 rpm came into usage.
Caught my attention at the time but I can't recall what it was now
Maybe something to do with relative speeds on optical soundtracks perhaps? I think someone pointed out that 33+45 makes 78 as well but I don't think that it had a significance.
I hadn't thought about the cost of materials previously but it makes sense. The whole "Reproducer" could be lighter now including the software [ie the Records]. [which didn't break] and you could get 22mins + on each side at 33 rpm. Very handy for getting 2 albums on a C90 cassette tape.
Dave W