Those dungeons are for new people and I see those new people having trouble with it, healers not knowing how to heal, tanks losing aggro and dps missing their 2 buttoms rotation.
Making it harder would frustate that people.

We already got a lot of reward by doing them and it takes very little time, and if u are bored of them, dont do them.
As stated above, leveling roulette was implement to help new players doing their dungeons, not high level players.