The Federation likely left them alone after the initial poor encounter with Voyager (assuming the Federation exists).
Of course, one possibility is that the Kyrians and Vaskans have had no further contact with the Federation because the Federation may have ceased to exist at some point prior to the 31st Century. (The character of Daniels from Enterprise was born in the 31st Century, which confirms that humans still exist at that time and are aware of the Federation. Also, the existence of the Federation Timeship Relativity in Voyager demonstrates that the Federation existed canonically to at least the 29th Century, )
For the remainder of the question, let's assume that the United Federation of Planets still exists in the 31st Century, and that it still follows the same guiding principles.
The USS Voyager
makes it home in the final episode, "Endgame",
which means that Starfleet and the Federation have access to all of the data collected by Voyager and its reports on encounters with various Delta Quadrant species.
Given the clear history of unrest and warfare between the Kyrians and the Vaskens, and the boarding attempt by the Kyrians that resulted in the deaths of three Voyager crew members and the kidnap of Seven of Nine and one other, it is reasonable for the Federation to conclude that opening further lines of communication with the Kyrians and Vaskens would have to be considered very carefully, if at all. As significant progress towards stabilizing Kyrian / Vasken society seems to have been made only towards the very end of that 700-year period, contemporary Federation intelligence may not present a better outlook than the original Voyager reports, and even if the Federation noticed the signs of progress, they would proceed very cautiously (possibly with secret observers, for which there is precedence in the TNG episode "First Contact").
In particular, the Federation would note that attempts at forming ties with the Kyrians and Vaskens might ultimately involve taking sides with one or the other, a situation that the Federation would prefer to avoid.