Short version: The admin made people feel unwelcome, unappreciated, and unwanted. And he made a habit of disrespecting them when they didn't follow the rules exactly as stated.
Long version: Here's just one example. The one that made me leave and start this site:
I posted an engine swap for sale in the classifieds. I went into all the details, spending a lot of time describing everything. And at the end I said "local pickup only, I won't ship this swap." Well, my my post got deleted and replaced with a message "This is an international forum. You must be willing to ship."
What? Ok, so I guess I missed that part in the rules back when I read them after joining over a year before. And now I have to re-type the whole friggin thing again because now it's all gone. So then I posted another ad with the title "Ok, I WILL ship this engine" and re-typed it all out, explaining that it was the second time posting since my first one was disrespectfully deleted.
Well, that started a mess. The Classifieds moderator IM'd me saying he wasn't the one who deleted it, and that he was sorry, and that whoever did it will be called out. So then some behind-the-scenes discussions went on, turns out Steve was the one who nuked my ad. On top of that, he didn't like the way that moderator talked to him, so he fired him. And then soon after, he removed the classifieds section completely.
That was it for me. The moderator told me what happened, and I emailed him back and forth about an idea I had for a new site that would mimic the Resource, but would be open for the users. They would have complete and open input into the site, offer suggestions, vote, and generally feel welcome. Like a tight community. Well, I didn't get the best feedback. He pretty much said it was a terrible idea. So I didn't do it. Then other things happened at the Resource. More things. And I couldn't take it anymore. I defected, started this site, and here we are.