Answer: New York's 16th District was not that progressive
Nathaniel, I won't shy away from what I see as the big weaknesses for Bowman: Democratic progressives right now are upset at incumbents for the high cost of living and America's pro-Israel policies, so it's likely he lost some votes there — as evidenced by a projected decline in turnout from his constituency (from 90,000 votes in 2020 to around 70,000 today, if I reverse-engineer the AP's "expected vote" math).
But the bigger, um #ackshually answer I'll offer is that he was never that popular in the district. In 2020, when Bowman won his primary victory against unpopular incumbent moderate Democrat Eliot Engel, he won by only 14 points. And in 2022, he faced no real primary threat, inflating his appearance of a dominant incumbent.
The money spent for George Latimer by outside groups, of course, also likely has a lot to do with tonight's results. PACs don't spend over $20 million in U.S. House primary elections for nothing!
—G. Elliott Morris, 538