YouTube is only one section of an entire corporation.
It's a corporation, not a charity. They don't spend tens of billions per year out of good will.
Ads were fine, the ads now are not fine.
Ads were not making enough money to justify continued operation.
They were successful when they were less intrusive, why do they need to do things this way and break up the videos when they have grown an empire on what was previously done?
Because "what was previously done" is not sustainable.