It's not even really supposed to be random so much as tossing you into whichever group has been waiting the longest for your role. I'm not sure why it would necessarily be those specific dungeons, but I guess AK would get a bit more traffic since it comes up in Animus books and is part of the relic quest. Early dungeons tend to get more traffic in low level roulette because of the number of people leveling straight through as well as those only leveling a bit to get cross class skills. I think all or most of the dungeons come up in the Animus books so that should be a wash I think...