Yes I agree, it is amazing to do it with comparatively so few cores. I’ve heard well-informed guesses that that’s why there is no Mac Mini yet with M1 Pro, because it would mean recent Mac Pro’s are left looking a bit sad and dejected.
It probably has more to do with optimizing your supply chain to as few SKUs as possible when there's a chip shortage.
Example would be Apple prioritizing their bill of materials for newer iPhone 13 SKUs rather than older iPhones. Margins are better and makes the supply chain less complex/expensive.
As the M1 Pro & M1 Max have fewer parts available then just focus effort on the MBP. I would not be surprised that MBP 14" & 16" sells more units than any M1 Pro or M1 Max Mac mini.