system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Where the Hell are the Xindi?!

Since Captain Archer stopped the war with the Xindi, they've been dead silent.  Even during the Dominion war, when the entire Alpha quadrant was at risk, the Xindi remained quiet.  Apparently, the Xindi are meant to join the Federation by the 26th century, but I haven't seen or heard a thing from the Xindi throughout TNG, DS9 or Voyager.  So where the hell are they?
gpt
Best bet? After learning of the Sphere Builders' treachery, they took stock of what had happened and chose to retreat deep into their own space to attend to old wounds and rivalries. While the original Xindi Council was a massive step forward in unification and peace, the actions of the Insectoids and Reptilians revealed that they had not progressed as far as they thought, and that, absent the false threat of Earth, they needed to go back to square one. 

Azati Prime became a neutral territory, where any Xindi could live and work. Generations went by as the Xindi learned how to live with one another, how to give up on their ancient tribalist ways, how to become one people. Because of the social instability, technological advancement slowed. Integration programs were put in place, to ensure diversity in Xindi environments for all of the species. 

It wasn't until a few hundred years later that the Xindi finally emerged a unified race. They opened up talks with Earth, now the Federation, and were allies for some time, before the invasion of the Sphere Builders brought them together and the Xindi applied for membership.