starting up your pc is free
exiting your home is free
going to sleep is free
starting your car is free
if someone put ads when you tried to do all of those things, would you complain?
You bought the PC, therefor you own this product and given the producers money.
It is your home, which you bought/rent, the producers got their money.
Sleep is something they cannot monetize yet and on top of that is a natural need of humans. You can't stop someone from sleeping, they will die.
You bought the car already, you bought gas, the producers got and get their money.
Youtube is a free service and if you want them to upkeep that without having to pay one penny..
Of course there are alternatives like showing ads on the side and not IN the video, but this way is more effective (though a hell lot more annoying) and i think they can get more income that way.
Anyhow, Youtube got to keep up the servers for everything, keep improving stuff, which means they also got to pay people to work on it.
For the viewer it is practically free to use their service.
The only thing you might pay is some time on advertisements.
As for the youtube partners, they make more videos or are at least able to make more/better videos because of that income they get from youtube (ads).
Yes, advertisements are annoying like they are currently and i am sure there are other ways to advertise.
But it is a free service to all viewers and if you want them to keep that up, you gotta pay with something else then money.