It appear from flight status UA held the plane 25 minutes for "passengers with tight connections", so the intent well after the OP boarded was to wait for some of those connecting passengers ( United Airlines Makes Connecting the World Easier Than Ever with ConnectionSaver )

However what appears to have gone wrong is once UA/GA decided to wait no longer, OP (on board) did not get "upgraded" and notified. Suspect the plane had been held for the connecting so long, the GA was rushed or did not want to delay the flight any longer to do the "battlefield" upgrades.

So attempting to do one good deed, another good deed was not done.