There's a world of difference between "there's an audience, and somebody might be able to find an effective way to extract cash from that audience" and "If You’re Passionate About Something, You Can Make a Living From It Online".
Remember when the dot-com bubble burst? The fallout was littered with sites that had audiences, but no effective means of monetizing.
The bubble companies had no intention to monetise their audience. The very phrase 'burn rate' is indicative of why it was a bubble. Their plan was simply to grow audience, even at a big loss, buoyed up by huge valuations and ridiculous IPOs.
Most of the dot-com failures were just straight out bad businesses, making a loss on each unit but making up for it in volume. Pets.com is the obvious example, selling cases of dog food at a loss because the shipping cost more than the dog food. The common theme of the dot-com failures was the desire to grow as big as possible as fast as possible, regardless of everything else.
A niche audience is completely different to a mass audience. They are inherently valuable by merit of being a niche. A list of pet owners isn't worth very much, but a list of people who own German Shepherds with arthritis is. The reason should be obvious to anyone who has ever sold anything. Just the list of names is worth proper money, let alone the community and the goodwill and trust that it carries.
Remember when the dot-com bubble burst? The fallout was littered with sites that had audiences, but no effective means of monetizing.