In some ways it does but my fellow keyboard hobbyists seem to have an infinite appetite for artificial scarcity. 99% of aluminum keyboard cases are barely distinguishable from one another but some of them cost a few thousand dollars while others cost $80. There are some with a better fit and finish but the higher in price you go the more rapidly the diminishing returns set in.

Occasionally there's some innovation and slowly we're seeing some of these innovations from individual designers get copied by companies more capable (and more importantly, willing) to mass produce things.

Split keyboards have different cases and boards. Only switches and keycaps are shared.