it is so annoying they pop up in the middle of the vids
That just means they're making a lot more money.
They just make allot money
Because they're taking every opportunity they get to make more money. YouTube is so depressing now, not just because of the excessive ads, but they don't feature channels on the front page anymore for everyone to see; now the only people who get all views are the ones who are already have millions of subscribers. :/
It's for money & social activities.
It sometime may helpful to your needed things.
Since April 2012 YouTube expanded it's partner program to everyone who has at least one monetized video. That means now much more people can enable their videos for revenue share and show ads in their videos. That's why you see much more ads on the videos on YouTube now.