And then I clicked on the most recent issue (194 no 3). Not hard to spot Alweis and Lovett (IAS), though admittedly a better mix here.
194/2 gives Daniel Tataru (IAS), Sung-Jin Oh, Josh Greene, Cole Hugelmeyer, and Jinyoung Park (IAS, but not a good example because I think the article preceded the appointment).
"hardly an article authored by a Princetonian"? please.
What connection does Tataru have to IAS? He was a visitor there in the 90s, but is there anything more recent? If we count all former students and visitors, then a sizable fraction of all (US-based) top mathematicians are connected to Princeton, so it's no wonder that many Annals papers are written by them. I don't claim there's no Princeton bias, but I don't think it a large one.
About MB, I don't find his work on higher composition laws terribly exciting either (though I could say the same about the subject of many other Annals papers), but that's not the only thing he did. Did his Fields citation even mention his early work on composition laws?