Why use the same tire all around

My riding is sharp high desert rocks, hard pack, fire trails in north AZ

I’m looking at new tires, so I’ve been reading everything I can find to help decide on 28s, 30s, Mongrels, Rage, Tensor, etc. So a few questions……

Almost every manufacturer builds their vehicle with wider tires on the rear. So other than for dune riding, why do people insist on putting the same size all the way around for trail, rocks, hard pack? It seems to me that if it’s better, manufacturers could save weight, cost, etc by doing the same by stocking and installing one size tire.

30s look cooler-no question, but they increase weight requiring clutch work. Is that weight any different from say a 2-seater to a 4-seater. A 2-seater with 30s weighs a hell of a lot less that a loaded up 4-seater with 28s. So is the clutch set up different on a 4-seater than a 2?