I understand (I think) why the NFL does not feel obligated to play preseason games on Sundays. There are no competing college games on Saturday, and besides nobody really cares about these games very much.
But why do you think they go out of their way to **avoid **Sundays? For example, this year, other than the Hall of Fame Game, there is only one preseason game (out of I think 64 total games) on a Sunday. I recall last year being pretty much the same .