Earlier quoted context omitted.
Same reason a coffee shop might offer to let you charge your phone/laptop batteries for free and then take that away when they see you are running an extension cord to your office.
So in this analogy opting out of ads is for who, exactly? Videos nobody watches anyways?
But it's not for people and organizations who are being funded to put up those videos. If you are deriving revenue from that video stream, whether or not it's a "profit" legally, then it's not unreasonable for you to be expected to pay for it. Advertising with shared revenue is the standard mechanism for paying for youtube videos.