In cross country the distance needs to be long enough to spread out the runners. In the regular season 8K is enough for the men but there would be people on top of each other at nationals if it weren't longer. Already (depending on the course) there are dozens and dozens of people finishing between 30 and 31 minutes, for example.
Should the women run longer? 8K instead of 6K? I'm not tuned into their results to say if they need to be further spread out. Even if they don't need to, I couldn't see a reason to have an objection to their running the longer distance if that's what they want to do. It would be silly to shorten the men's race for some misplaced sense of equality, though.