I think that the answer is that most UA *G don't know that they can access the lounge. Even with delays to the AC flights, it wasn't terribly crowded yesterday.

My overall impression of the new concourse was positive, especially compared to the old pier that UA used at LGA. I did note that the restaurants don't seem to have much seating, and the bathroom behind Shake Shack is nice, but seems like there is a lot of wasted space and that they could have a lot more stalls/urinals there. I'm not sure where the bridge from the main terminal will come in, but it seems like it will be on the second floor and everyone will go past the MLL and UC to get to the gates.