There's an article in The Guardian and in the comments someone called garythenotrashcougar wrote this (I'm sure on this thread others must have said similar) but anyway, I agree with it:
"It's not rocket science.
Liverpool's success over the last 5 years was built on ferocious pressing, led by a midfield of Henderson, Wijnaldum and Fabinho.
Those three used to smother teams and allow the full backs space to bomb on. It didn't matter it left them 2 v 2 or even 2 v 3 at the back, the ball would rarely get near their half never mind their goal.
Fast forward 3 years from their peak to today and you have three main problems:
1. Henderson and Fabinho's legs are going.
2. Wijnaldum left and was replaced by the more talented but less hard working Thiago.
3. Since 2018, Klopp has been far too loyal to injury prone and inconsistent CMs like Oxlade Chamberlain, Keita, Jones and Milner in favour of strengthening in that area; his gamble, which has turned out to be a fatal mistake.
All three issues have left a previously untroubled defence exposed, and it is currently crippling them.
Simple as that really."