I think it is yet another consequence of the American adoration of various aspects of English life. If I recall correctly, rowing blazers were a part of the early 20th century boat races at universities like Oxford and Cambridge. Brightly coloured and striped blazers, white ducks and straw boaters were usually parts of a costume that was commonly seen on young men who were either part of rowing teams, or part of their audience at races. Perhaps the same practices existed in East Coast Ivies and prep schools.I agree as the sweater and OCBD are the two items I like. The jacket isn't my thing, but I get that rowing blazers are a thing. However, that one is so short it looks undersized to my eye. Also, even though rowing blazers have a genuine history, who really wears them, and where do they wear them, today?
I guess there's a niche of old-line money that might still wear them, but who else does? It might have already passed - I'm never up on this stuff - but rowing blazers seemed to be a thing a few years ago with several companies making them, yet I never saw them worn by anyone.
I can't recall seeing these kinds of blazers out of the context of rowing events, whether in England or the US. How many of us encounter a man in such a blazer on the streets? We do encounter them in RL adverts, but that's another story!