When I first started flying Varig domestic in the late 90s, there were 2 FAs and a beverage cart moving up and down the aisle virtually the whole flight whether it be 1 hour or 4 hours. No one ever went without.

There is no reason this can't be done on UA domestic. It would cost a bit more in beverages, but nothing in labor.

BTW, when I'm in Y, I sit in aisle seats and get up as many times as I want to get more beverages/etc. from the galley. No remorse.