VC funding has a lot of problems. Funding via advertising is similarly fraught with peril, maybe worse, especially the most lucrative stuff. You can fund things by selling premium content or features, but this too is rather tenuous: if you are say, SoundCloud, one of your primary customers is inevitably going to be artists, who themselves are by and large not rich.
Not to mention, no matter who you focus your monetization on, $1 is infinitely more than $0, and monetizing useful features or access to content will inevitably lower the overall value of your platform. This is presumably part of why advertising is so enticing: end users don't have to "pay" anything. Sure, advertising isn't literally free, but users do not have to set up a payment method and take money from their account and send it to yours, which is a massive difference, and massively increases accessibility.
Then there's stuff like crowdfunding. Platforms that let you do one-off funding campaigns like Kickstarter or Gofundme, or platforms that let you do monthly subscriptions in exchange for "rewards" like Patreon or FANBOX. There even is a platform that is partly funded by monthly subscription payments (Misskey.io) and although I'm sure it is a relatively small part of the funding (at least I would certainly assume so) it still seems to have been successful nonetheless.
And that's just funding. What about structure? Becoming a non-profit or public benefit corporation is seemingly not any kind of sure-fire way to avoid trouble, as can be seen here. While I don't know exactly how the legalese works around a lot of these topics, it feels like these measures simply don't do enough to prevent corruption or at the very least, undesired future changes in direction. You want a company to have autonomy to carry out its vision and try to survive in the process, but you don't want it to compromise its core values in the process. Is there anything you can do legally and/or socially to provide better assurances?
This is very frustrating because I think a lot of us see the sad state of the Internet and want to do something, but it's hard to work towards it because you can also see a graveyard of good intentions gone horribly awry. There's all kinds of attempts to work around it, but as a wise man once said, "Mo Money Mo Problems". It seems that the temptation to exploit things always manages to find a way around your safeguards to prevent things from being exploited. Just to beat a dead horse even more, remember the last time you were excited for a Google product announcement, like say, GMail? I'm not saying they were ever a charity or intending to be... but it's hard to not see the painful way in which values that were once hard-fought slowly fade away. Somehow, eventually, everything becomes rent-seeking, a game to see how much money you can get back from an investment. One would hope there is a way out that doesn't involve a very painful upheaval of society, but over time it's getting harder and harder to believe it.
Even "winding down" doesn't necessarily need to be a problem. It's all in the "how" it's done.