If I had to guess this is exactly the reason; being that the customer who does not want the 'pro' part but is still willing to pay the price will go to the tundra or save a bit with a off road or trailhunter
Toyota refuses to allow us, customers, customize our orders. Instead they’d rather let the distributors load up the trucks and 4Runners with shit we don’t want or need. The priority is for their selling channel to make maximum profit. Their allocation system sucks.
Hopefully they avail the Extra Cab to a few more trims, especially as a (minimally different) TRD OR and a TH, especially with big-ass leaf packs and high GVW.
Of course, this doesn't help anyone with their fancy seats. 2nd row platform instead of seats would at least be useful.