How would you guarantee someone something like that?
Incorporate, NFPO, most likely 501(c)(7).
Besides that, I don't think they tried. "Do no evil" isn't reassuring in the slightest, especially to those of us who remember Reddit before Advance and Tencent bought in. This is when Reddit was literally user powered (image relevant). We bought gold for other redditors, knowing that the funds were directly supporting the site. Go take a look at how that worked out. "It's your site", "we couldn't do this without you", meaningless. I remember when they pledged 10% of annual ad revenue to non-profits, selected by the users. They really did the most to make the users feel like they were part of something special. We see how that turned out.
Obviously, support whoever and whatever you like. All I want to do is balance out the optimism. Real money is changing hands here, and some of us have been down this road a couple of times. Those experiences have taught me that it's at least as likely that the site-runners want to be rich and successful as it is that they can resist the temptation when it comes knocking, and that's being generous.
It's $1.99/month or $16.99/yr, which is waaayyy less than $3/month. Less than half that, if paid annually.