The explanation I've heard is that the national curriculum switched away from phonics and to a teaching method called "balanced literacy", and this went terribly [1]. IIRC it involved teaching kids to recognize words by their overall visual shape. I believe this is what mature readers do, but the problem is that for this to work, one first needs to have bootstrapped a robust vocabulary. And that happens via being able to sound out words, i.e. phonics.
(I'm not sure whether Cato is generally reliable, but FYI there are lots of other writeups online on the same topic. It was the first non-paywalled and reasonably complete one I found)
(I'm not sure whether Cato is generally reliable, but FYI there are lots of other writeups online on the same topic. It was the first non-paywalled and reasonably complete one I found)
[1] https://www.cato.org/blog/phonics-failure-public-schools