Back when UAL side got contract 2000, ALPA did a joint study with the company and the conclusion was that a second jump seat was cost effective. Getting more pilots to/from home without causing a Positive space seat in the back for last option commuter. So the decision was made to retro fit all UAL 737's and 757's the second jump seat. (Ferris bought those planes with 1 JS supposedly as vindictive retribution for pilots strike.)

Then backruptcy, and Glenn wouldn't spend a dime on anything, even stuff that was proven to save money, greviance was filed, still working I think. That's why only, 7 now, of UAL 757's have the second jump seat. Got that far installing it in heavy MX before Glenn put a stop to it.