(pure speculation) or, maybe they've got a 'Mac Mini Pro' coming using whatever chip they're cooking up for the high-end Mac Book Pro and iMac Pro.. or maybe e

(pure speculation) or, maybe they've got a 'Mac Mini Pro' coming using whatever chip they're cooking up for the high-end Mac Book Pro and iMac Pro.. or maybe even more than one of those chips. So in that eventuality they want to maintain the bigger case footprint and much-bigger-than-needed power supply.