Most of this has already been said, but here's my list:
1. Cost. I remember just a few years ago that we could get APs for around $700 per person. I think it's double that now.
2. Erosion of perks (free FP+, free airport transportation).
3. Politics. The country is split politically and Disney has made a conscious decision to be inclusive in some ways, but at the cost of being exclusive in other ways. I don't want to get into a political discussion here, but there are people that are turned off to Disney following the whole Desantis fight and other things.
4. There are other options with more value plus post-COVID travel is over.
5. Recent
DAS changes may have alienated or discouraged a whole bunch of families from coming.
I don't think it's the heat as it's been surface of the sun hot in central FL JUN-AUG for ages yet people filled the parks in the summer. To my points about cost and other options, even Universal APs are much cheaper than WDW APs. For those in or associated with the military, the cost is even lower. You can get a Universal AP for around $200.