If you're a new player, anytime you try to queue for older content that is rather rarely run, you would notice that while in queue, the spots will keep changing from being filled up and not being filled up.

If you're an older player, when you queue for roulettes, especially trials, the issue becomes apparent.

The roulette algorithm dumps you into a different queue every few minutes.

This is probably good for anyone who wants a fast entry into trial roulette but is pretty bad for anyone who is trying to get their clears on older content.

We've seen many instances of screenshots showing people with ridiculous queue times. I believe this is the main reason why.

tl;dr Roulette queue is bad for helping new people clear necessary content.