It's hard for me to get a sense of scale here, I wouldn't have thought that this sort of thing would require more than a token level of resources.
Everyone's charity has a limit. I consider shutting it down all the time but it becomes hard when I browse my own forum watching people connecting and writing. And losing money on this forum over the years is one of the sacrifices I've made which accelerated my return from the beaches of Thailand. Sometimes I look at that with regret. The forum cost more than my rent.
Using off-the-shelf software like vBulletin/Xenforo is expensive. You end up throwing money at scaling issues because it's essentially a black box.
I ended up migrating to my own software to wrestle control over costs. But it was an incredible amount of work to rebuild a popular forum from scratch. I could do it because I was in my mid-20s living off savings in Thailand. But I'm not, anymore, and I'm left throwing money at scaling issues again because it's hard to commit serious engineering work to something that isn't a profitable venture. The opportunity cost is huge.
I run a collaborative writing forum for mostly a pre-teen and teen demographic. It's the ilk of what got me into writing as a young one. They don't have money to spend, but ads keep the forum alive.
It would be extreme to say my forum has nothing to offer these youngsters, or that my lone banner-ad eclipses any good my forum may be doing.
As ads die, we're just going to continue witnessing the centralization of the internet which surely isn't all that great, either.