Unfortunately, there is a very vocal minority of gamers who scream this idea down. These are the people from which the "game-playing loser" stereotype comes from - the people that really do spend nearly every waking moment churning through long game after long game.
They flood forums and Amazon reviews, screaming at how a fantastic 6-hour game was a "rip off".
I think there are a lot of adults who lead productive lives and would love to be able to play games that are finishable in a normal person's available free time. But they're not nearly as visible.
An unfinished game is far less likely to be returned. You know, maybe some day you'll get around to finishing it.
I am on mobile right now, but search TIGsource for full links.
And to add to the discussion: games that I play the most are either online, procedural, or score-based. But games that I have enjoyed the most have all been highly focused, incredibly polished single player experiences. 10 years ago, these were long (30+ hour) games. But the cost of producing content has risen so much lately that you can only obtain this level of polish if you keep it short.
Game designers have created this logic that you must do X before you can see Y. If you haven't done X then you don't deserve to see Y. Yes, it can make it 'too easy' if you can skip anything, but I'm the one here making my own entertainment. If I've already read a novel and want to skip a chapter that was boring, I can skip it with the turn of a page. No author tries to stop you from doing that. Same with a movie. Just press Fast Forward.
If you ask me, the best driving game of all time was Outrun. It plonks you in a Ferrari at the start line of a race, and you drive as far and as fast as you can in the time allotted. The more you play the game, the better you get, and you're rewarded by being able to see more of the world, but it doesn't reward you for just slogging through.
Since that is not going to happen, I have a hard time agreeing with your wish that developers make shorter games. I mean, I'm not exactly in the poor house, but I'd balk at paying $60 for four to six hours of gameplay, even if that was a pretty amazing four to hours.
Also, cf. movie theater prices.