It depends on what you have unlocked and available. If you queue for Alliance on a sub 60 job or without having done the quests to get Void Ark/Mhach/Dun Scaith, you'll be getting a lot of Crystal Tower because it can't give you anything else. My friends and I tend to call that one "Labyrinth of the Ancients roulette" because of how often it comes up.

They're all like that. Trial gets a lot more options once you unlock things like the Warring Triad, all of which are optional, to give it more options for you to get. But the basic MSQ ones come up a lot because anyone doing the MSQ now will need them and they'll get others to help fill the party out.

Expert only has two, so RNG could easily give you the same one five times in a row.