You hear stories of Jim Brown playing every minute of a preseason game. But even as little as 10 or 15 years ago, the question was whether stars would start the second half or not. In recent years, the NFL's best either sit out the entire game or post some ridiculous stats. The leading rusher in the league might have 2 carries 7 yards by his name in the box score of a preseason game.
It has affected the regular season. The first week has always produced great material for the Football Follies. But the level of play at the outset of the season has decreased noticeably. The first weeks have less to do with talent now and more to do with continuity. If you have the same system as last season, you have even more of a leg up, because the amount of game experience new players have to get adjusted to a new system before the regular season has decreased sharply.
Yet the preseason is as popular as ever. It's have people are too dumb to notice the miserable product being put in front of them. Preseason games sellout. People skip parties to watch the 5th string running back break off a long one. It's absurdity.