I would say the RLL is both a bidding option and a contingency solely because you must select that condition in PBS in order for that contingency to be executed should the circumstances warrant.

For those who have stated they have tried for an RLL and not been awarded one, that isn't surprising. You would only be awarded one if:
1) You were above the published RLL number; and
2) You opted for the RLL condition in your PBS bid; and
3) Your last bid grouping had no restrictions (avoid, prefer off, etc); and
4) There were not enough trips remaining in the PBS pot to build you a line within the LCW.

It is number 4 that makes the RLL so elusive. If you have any seniority above the published RLL, there are likely enough trips in the pot to build you a line within the LCW if all of your negative preferences are removed. And yes, I suspect the remaining trips in the pot at that time are less than desirable and likely non-commutable on one or both ends.