I don't disagree with you, but just from a devil's advocate point of view, some would argue that by using ads to pay for the content, it allows the content to get to those people who couldn't have afforded to pay for it themselves.
> Or, niche topics that can't draw enough support to stay afloat
This isn't specific to adverts and applies to every industry/endeavour that depends on voluntary engagement for funding. Name one thing that does not require a minimum level of popularity to be self-sustaining
