The dealers order the trucks. Not the public. What the dealers want and what the public wants aren’t always the same. If more manuals were offered more would be sold. If they ordered 20% manuals they would have all been sold. They are cramming auto trannys down the public gullet because a take or leave it attitude is easier for them to deal with.
Those 20% manuals would mostly have been sold at a loss. The driving populace simply does not want manuals in most trucks at a significant rate to continue to produce them. Again, Ford had manual transmission versions available for order by anyone, not just what the dealer itself wanted. They had an abysmal take rate and many dealers who had manuals had them sitting around for more than a model year - a friend got a Dodge Ram 2500 with a manual transmission that way. Popular configuration vehicle except for the manual. It sat on the lot for 14 months. The dealer took it in the shorts just to get rid of the thing.
So, no, it’s not just because “the dealers didn’t want them” it’s because the public *and* the corporate fleets didn’t want them even though they could have easily ordered them.
On top of which, there’s also the technical problem of mating a manual transmission to today’s very powerful engines. A clutch capable of dealing with 900lb-ft of torque is going to be very heavy; a manual gearbox of similar capability is going to be ‘agricultural’ at best. People don’t want that in their trucks.
You're delusional.