For Tribes, one of the things they did was make it pay2win and then introduce OP weapons that could realistically be unlocked by paying (unless you invested insane amounts of hours playing the game to unlock them). People who paid were stomping those that didn't, causing players to leave the game. It took them a long time to undo this, but by that time the game was dying regardless of what they did.
Another thing they did was to introduce a speed cap in a game that's about going fast.
They made promises that they didn't fulfill, like releasing modding/mapping tools or being dedicated to their game. Removed Oceanic servers despite there being a healthy playerbase there. There's probably other issues, but these should be the major ones. Watch this:https://www.youtube.com/watch?v=6Srff0L5s6w