It's not that the position is unpopular its just that since we accepted a pay equalization between 757s and 737s there is no longer an incentive for junior FOs to move from 737 to 757 unless they are senior enough to hold international trips.

I never thought about this before, but it could be a real problem for new hires placed in that position. They could stay junior for an exceptionally long time because pilots just senior to them might wait and bid 756 only when they are senior enough to fly international, and that process might take a while to conclude.