Slap Shot
I got nothing
At least with the preseason games, they're basically required purchases for season ticket holders, so you either 1) had to buy them to get your regular season tickets, or 2) were given them for free by someone else who had to buy them and you might as well go cause free ticket.
I honestly don't know anyone who buys a single game ticket to an NFL preseason game.
Are they measurably cheaper? It might be a chance for a dad to take their kid to an NFL stadium to get the experience (albeit watered down greatly) without the full cost of a regular season game.