If processed as a standby, you have to clear into the flight before a GA will add you to the upgrade list. In my experience, even when it is clear that I will clear the standby list (such as when I am first and there are multiple seats left), the GA will clear all upgrades first before clearing the standbys, so even if I would have cleared to F if I could have gotten on the list, you usually end up sitting in Economy. On the other hand, I am usually so pleased that I have a seat at all, and usually I can get a decent E+ seat that opened up by the person cleared to F, I am usually ok with it. In this case though with empty F seats, like the OP, I would have also been quite miffed about it, perhaps undeservedly, but I think that is the normal human response.