FPS games getting shorter?

Back in the day I remember delta force 1 and two were really long games. However I noticed that the games today are limited to 12-15 missions max. This seriously blows....

FPS games involve a lot of 3d graphics.  Typicaly the texture resolution and poly count is higher than other games.  With these budget costs you don't get very long games.

It is more profitable to sell a very good looking game which secretly only lasts 8 hours than to sell a bad looking game that lasts longer or actually has good design.