Others have already clarified that the roulette is working as expected; in short, the goal of the roulette isn't to give you a random experience, it's the game saying they'll give you rewards in exchange for doing the content another player wants to do.

Quote Originally Posted by Novaura View Post
But getting these same dungeons every single time with no variety has resulted in me getting bored of the game because nothing interesting comes up.
With respect, if you want variety, remember that you have the ability to intentionally queue for a handful of dungeons that you haven't done in awhile.