Are you confusing revenue and profit? Wikipedia, OpenStreetMap and Lichess are examples of successful non-profit sites. They have costs, they have revenues, but they don't exist to generate profit.

>but also a guarantee to your community that the product will still be around in a few years and not turn into a rug pull

There are no guarantees. Think of all the perfectly good websites that got shut down not because they weren't financially sustainable, but because they didn't generate enough profit for their owners. Google's graveyard is a good place to start.

Or the sites that were profitable, so they then they got bought out, and shut down, because what the owners really wanted was money more than anything.

Clearly the site in question here is not currently sustainable. But attempting to build a sustainable non-profit website is not impossible.