"Don't you hate those videos that are 5x longer than necessary? WHY ENCOURAGE THAT?"
From googles perspective it's because they don't care about the user, and are cowtowing to the advertisers. Longer videos mean more ads, which means more $$$.
I wish google had never bought youtube... I knew they would ruin it eventually.
I think the real discussion here though is more meta than just google... we have allowed advertisers to gain way too much power on the internet, and if we aren't careful they will ruin us just like they did newspapers.
This isn't just advertisers though, this is the general business model of internet companies. Here is the pattern:
1) Create cool new thing, with no ads, no tracking. Users love it and it spreads like wildfire.
2) Slowly boil the frog. Start tracking users and selling user data to third parties, justified under esoteric EULAs and TOS. Start small, unobtrusive ads.
3) Make the ads more prominent, more frequent, and harder to skip/ignore.
4) Allow your platform to be used as a corporate promotion tool that's more like sockpuppet central than regular advertising. Bots talking to bots, subtle corporate products in memes, etc.
5) Now that you have completely aliented the userbase, now is the time to ramp up all of the above and then go public, ride the boom wave up, and at peak sell a massively overvalued company to some dumbass group/company/people, run away with the cash, and take video of your product as it burns to the ground.
The users will stick around until someone else starts at 1 and does the same thing but under a different name.