My opinion and all the evidence I've seen is that It's because AOC wasn't vulnerable.
Polls from March show Bowman was already in trouble as far back as March. Bowman's campaign (the Upswing research poll) showed Latimer and Bowman were essentially tied. That's bad for an incumbant. The AIPAC poll from the Melman group around the same time showed an overwhelming preference for Latimer over Bowman. That's when the AIPAC started pouring money in to the campaign to exploit that weakness.
The AIPAC research showed Bowman was vulnerable, similar to why the AIPAC is spending big to replace Cori Bush but they are essentially leaving Ilhan Omar (so far).
The AIPAC analysts are highly skilled at collecting and analyzing data. This allows them to know how and where to spend their money to get the maximum return on their investment. They aren't going to waste money trying to defeat a candidate like AOC who is still largely popular with their constituents.