Yes they are doing this to some degree in the US, however, most lead to failure since car dealers typically do not pay well and have greater employee turnover rates.

For some odd reason there is a pocket of in-house dealership tinting successes going on in the mid-south of the US.

Too true!
A lot of people haven't bought new cars for years so when the sales person hooks up the deal finally, he then must introduce the buyer to the "aftermarket gunk girl" whose job it is to sell all the accessories that stop the car falling apart....BS

One of those items is window tinting.

It then becomes easier like you said to organise all this "at point of sale" for the customer and many just include the value onto their lease payments so it doesn't hit the hip pocket nearly as much.

There is also a very misconception that dealer film must be better because it's "factory tint."