I think it's just the opposite; a product or service that you charge money for is way easier to make a living from than an ad-supported community. How big is the market for ad-supported communities for fish tank owners that are big enough that you could live off of them? A dozen or two? But how big is the market for companies that make a product or service that fish tank owners would buy? Probably thousands. Depending on your margins, you can make a living off of a handful of customers if you're selling them something (and you make money from the very first customer), but it'll take a large audience before you can make any money from ads. This also ignores the fact that ad-supported models have both users and customers, and they're not the same group, which can create all kinds of problems.

Identify a problem, create a solution, and ask people to pay for it.