It was hugely popular before being free. The problem was that some basic options for the classes that were strictly better or required for gameplay (the worst offender here is likely the Jackal[1]) were gated behind days of grinding or microtransactions. Newly introduced options usually had some severe balancing issues. The core audience and biggest advocates for the game were people that played Tribes and Tribes 2 decades earlier - they didn't really like that they couldn't buy the game outright and have all the content in it unlocked at a reasonable pace.
[1]: https://tribes.fandom.com/wiki/Jackal