Lets speak about Mentor's.

[Avatre]

[...] or they realized they didn't have time for this duty,[...]

To be completely honest, nobody should queue up for Mentor Roulette unless they do have time for ANYTHING that could pop up(best to have 1-hour you can devote to whatever you get). While other things do pop up(family emergency for instance), there really is no cause for mentors, aside from afore mentioned item, to just drop the instant they zone in and see that it's an EX primal(lets face it, those are the things that most people drop instantly from)