1. Coaches generally view pre-season games as a waste of time. The game planning is a significant distraction.

2. The risk of injury outweighs the benefit.

3. Joint franchise practices provide a better opportunity for player evaluation, including 2/3 deep + practice squad.

4. Joint franchise practices provide a better opportunity for evaluation of position coaching and coordinator play calling (eg the pats identifying a successor to Josh Mcdaniels this year).

I think some of the points you made were valid in the past, but are now a dated perspective.