Your point doesn’t make sense. Even back when people where creating their own services and sites (which they still are, it’s not like that has ever stopped) there was still often ad-funding when those things grew to a scale where donations alone couldn’t support them.
And yes, lemmy is ad-free. That’s doesn’t mean the model will work for everything else. Ad-support can be a great way of keeping something accessible and free for people who can’t or won’t pay for it. It’s not always a bad thing.