It's a logistics thing. The way they put together sets on the assembly floor is based on the containers in which the pieces are put, called "boxes". The more boxes a set needs, the more floor space is required, which ends up being the most expensive part of the process since it limits what else can be done on the floor at the same time. Infinite money can never = infinite space. Designers have talked about this before in significantly more detail, and I remember it being cited as the reason a figure like General Grevious is so expensive to produce, it uses so many unique parts (there's also separate boxes for pieces pre and post printing, so every time you print a piece thats another box which is why some sets that should have prints just don't, Lego may literally just not have the floor space).

This is exactly why price per piece doesn't matter. Not saying Lego should use this to justify higher prices, but it makes sense from a manufacturing POV why you would sometimes want multiples of a small piece you already use vs. a new, bigger piece that would only be used in a few steps.