These players have played a ton of football and how much practice does the second string really need? The preseason games are just an excuse to make money. Two game instead of five is more than enough. I'll go as high as three for the sake of judging the players on the fringe.
The preseason games have become more and more important as your comment that they have played a "ton of football" is missinformed.
The players union has required that less and less full contct with pads occurs during practice leading up to the preseason and regular games.
These game are some of the few opportunities the coaches have to see these new guys going at it full steam.
Your lack of logic is staggering. The Players union wants less rough practicing to reduce injuries and trust me they've all played plenty of football.
And coaches can get really good looks at guys in practice in the first place.
Also, if the players wanted more games, they'd have upp'd the season to 18 game and 2 preseason as was proposed. But,they don't want it cos they don't want the added injury risk. Hence why they barely play in the preseason too.