Holding back upgrade inventory until departure also pretty much ensures that 2P's won't get one unless it's an off-peak time. As a mid to lower tier elite, I appreciated that I had a shot at an upgrade on UA rather than the EUA system on other airlines which heavily favors gold/platinum members.

That being said, if UA can increase revenue by selling F seats that were previously being allocated to upgraders then they should do it.

This may be the nail in the coffin for my allegiance to UA. Upgrades are one of the FEW differentiators of 2P/1P status vs being a general member. (I don't count E+ as a difference since anyone can buy into it.)