It’s called capitalism. You build what will sell. When any option falls under 12-15% of the orders, it gets cut. In other words, if your orders are 7% manual transmissions, you can’t afford to offer one, stock clutches, shifter linkage, pedals, transmissions, etc.
The last full size trucks for Ford and GM with manuals were 2006 models. Dodge made them quite a while after that for one reason, the failure rate of automatics behind the diesels, their transmissions were junk.
I’ve managed new car dealerships since 1990, nobody wants a stripped down truck. Or car.
Car dealer = shyster.