Makes sense to me (but I'm of course biased) due to selection bias. My impression is that those for whom APL clicks, find the day-to-day APL experience very enjoyable, while those that just don't get it will tend to leave APL behind. Probably not so for more widely-used languages, where people will stay with them, even if it means daily frustration.

Only about 500 people filled in APL, whereas about 22k people filled in Java. For a lot of people APL isn't really on the radar.