Well, F2P games spread by word of mouth and profit over time. Word has it that Battlefield Heroes made millions, and is still thriving.
A true successor to Tribes 2 would result in modest intial sales, followed by years of community activity with no profit. The whole idea of creating a one-shot quality game hoping for massive initial sales simply doesn't work anymore. Either you keep pumping out games one after another, or you create games that increasingly profit over time.
That's why there are more than one Battlefield, Call of Duty, and Crysis. They can't financially survive as one-shot games. On the other hand, F2P's and MMORPG's increasingly profit over time. There's no way for a revamped Tribes 2 to survive today's landscape without losing money.
It should be noted that Tribes Acend exists for only two purposes: advertisement for Tribes Universe, and a profit-generating muse.
In other words, their target audience is the masses of new players, not the tiny Tribes community. Who gives a shit what Tribes players want if the majority of their profit will come from new players who will enjoy the game, as opposed to the small number of angry veterans whose demands will turn the game into an unprofitable mess? Ultra-niche doesn't work in gaming.
They want easy to play, low entry barriers, masses of new players, big profit. It's called business.