Why are videogames so short now?

Yesterday I finished Medal of Honor: Airborne, and I have mixed feelings: It is quite impressive and you almost feel like if you were in the middle of WWII, but... the game didn't last me one afternoon!!!

Why companies release games so damm short?

I can think of few reasons, but none of these are really good excuses...

• Development costs are high: Ok, now doing a AAA title is like producing a Hollywood movie, but once you have all the assets (sounds, graphics, and some levels designed), why not spending one or two more months creating additional chapters? As a player, I feel cheated, like if I bought a really beautiful videogame, but which smells like released in a rush.
• Designing a level is not easy: Ok too. Neither easy to do it "fun" nor to do it quick because the increasing level of details... but why not repeating some level designs with different makeup? Changing textures, enemy types and effects you can give it a different look... Hell, Wolfenstein 3D had tons of levels almost with the same GFX!
• Schedules: Worst excuse. As a player, I don't mind if I have to wait further if I know I'll be getting a better product. Mass Effect has been delayed at least two times, but it looks it's being really polished.
• Modding is available: That would be great, if MoH had modding options ;) But as most of EA titles, it doesn't (at least officially supported and provided), so doesn't applies here.
• Designed for console: This is a (bad) excuse sometimes I've heard from friends. Gran Turismo or Final Fantasy series are quite long games, so find another better excuse!
• Designed for casual players: Another increasingly typical excuse. What are difficulty levels for? Making a game shorter doesn't mean it'll be better for casual players, means shorter game experience.

Any other excuses you know of? Any good reason except costs for developing a game that you can finish in 5-6 hours?