Fixing reserve rules seems like a potential win-win for the pilots and the company. The recent unfilled captain vacancies indicate a problem exists. If U wants to resolve said problem, it seems they have three options: (1) increase pay to a point where pilots are willing to suck up unfavorable reserve rules (high cost); (2) rely on TDY coverage (unpredictable); (3) amend the reserve rules (not sure what the impact/cost would be...would amending reserve rules be expensive?).
Having more folks upgrade to the left seat or to a widebody assignment appears to benefit both sides of the negotiating table, so why would this be so hard to iron out?