In fairness I made the original accusation. I saw IIRC a John Burns version with all the edges smoothed out at a guitar show in Brum years ago and it looked gorgeous.
Personally I think like lots of bands they just ran out of creative steam.
As for U2, as long as the juggernaut keeps filling stadiums they'll keep on releasing dross which doesn't have to be the case; Genesis proved that with their tour in 2007.
I love their output between Document and Automatic For the People, even Monster and Up were good.
I recently browsed the rest of their albums and was shocked at how awful they were. They probably hung around at least ten years too long.
I like the early stuff and All The World... and Exit... are great representations of that stuff. My favourite would be Signals even with the mushy sound, IMO anything after that was $h1te, not helped by the weedy Wal/Steinburger tone.