Of the about 40 that I've adopted, I think at least half were done that way.
As for doing it "just because," I like to get things straight so that other people get their "just desserts" as well. If there's a problem & others aren't getting their badges, shouldn't it be fixed?
[edit] After posting that, I went thru one line of ancestors with a somewhat unusual name (Gummel) to see if any were orphaned. I found 2 that I adopted as a "group" & sure enough the "Big Heart" badge showed up. I don't think I did anything different than I had done before for some of them. If there's a "secret" to this, it still baffles me.