> I present the full list of possible answers
Not included in that list and thought up in five minutes:
(Assuming first contact unlikely when only one civilization at our current level of development or earlier is trying, and intergalactic communication is too expensive to bother with at all.)
"We're not one of the cool kids"
1. First contact seems exciting before you do it, but is actually just really boring/dangerous/confusing in hindsight.
2. Our most likely first contact partners are in the more dense area of the galaxy.
3. Their best first contact partners (our rivals) are most likely in that same or an even more dense area of the galaxy.
4. Everyone else in the galaxy meets up with someone else first, and after that loses interest, and doesn't try to contact and and just ignores us.
Alternate, related "Bumpkins last":
1. Galactic civilizations are likely to focus searches for other civilizations towards the galactic center (because that's where the greater densities of stars are, so you get more results per area of sky searched, or due to some yet to be discovered reason causing greater expected payoffs there).
2. Other civilizations are likely to be closer to the center of the galaxy than us (because that's where more stars are).
3. Ergo, other civilization(s) are most likely looking and broadcasting "hello worlds!" messages away from our tiny backwater, towards the galactic (urban?) core. (Or at their plentiful urban core neighbors if they're in the posh neighborhood.)
These are related to some of the ideas on the wiki, but they are still distinct. (See "Matroishka brain" for another "Eh, not worth the effort," explanation.) These two probably aren't very cool or likely, but I would contend that they meet the stated criteria of "not on that list" and "thought up in a few minutes."
I hereby demand my honorary diploma in Fermi bullshitting!
(Seriously though, I agree, some people need to check wikipedia before filling up this thread.)