Sorry if I wasn't clear - these lunches have nothing to do with work. I eat lunch sometimes, my colleagues eat lunch sometimes. Sometimes we go out to eat together and socialize. Work doesn't enter into the equation. We lose that benefit when going fully remote.
There is value to me in having lunch with my current colleagues. I also get value out of having lunch with my ex-colleagues who are now just my friends in the same city. We still have lunches together. I am thankful that I used to work in the same city as my colleagues so that this is still possible!