The pandemic is likely responsible for a lot of it, even though people don't want to talk about it. Covid is proven to reduce IQ, every infection is damaging the brian and the key finding is that people aren't aware its happened to them.

https://theconversation.com/mounting-research-shows-that-covid-19-leaves-its-mark-on-the-brain-including-significant-drops-in-iq-scores-224216