Bigger chips = more distance to cover for your electrons = more power required = more generated heat = slower throughput for your data.

Surely you don't believe that the entire chip industry had not thought of "wait what if we just make the chips bigger".

AMD hiding Threadripper behind their back: Uh yeah what a terrible idea, we definitely didn't actually do that. Making a CPU that's twice the size, how ridiculous would that be right?!