this sounds ridiculous (and it is) but there are two waitlists:

one that handles upgrade requests made before checkin (GPU/RPU/miles/advanced CPU windows) and one that handles upgrades at the gate (battlefield as we call it). as i understand it, when the flight goes to gate control, these lists merge into one with some unclear level of upgrade prioritization at that point.

you are on the first list, which is not publicly visible. when you check in, you will see yourself on the 2nd list, which is the one you can see on ua.bomb.

as aacharya notes the people you are seeing on the publicly visible WL are probably already checked in from connecting flights that depart within T-24. you will appear there after you check in, if your UG has not yet cleared.