I have a theory/observation, and it may be totally off.
I think Eddie works hard, cares deeply for the club and players, and gives everything, but he can't break out of a certain mindset.
He holds so rigidly to the 433, high press style. He's so risk averse in the transfer market, and seems to want so much control. He's so reluctant to rotate, to make subs, to play youth.
At a stretch you could also say he tends to move players into more defensive positions, rather than attacking ones - off the top of my head, Woltemade ST to CAM, Ramsey CAM/LW to CM at best, Hall CDM to LB, Joelinton ST to CM, Miley CM to RB. Not saying some of those haven't worked, but they're all defensive moves. I struggle to think of many who've moved to more attacking positions.
I suspect Eddie can't or won't adjust his mindset on a lot of things, and when plan A doesn't work, he doesn't really know what to do, and in matches, we see the players kind of pick up on that. Hence the sitting back, inability to control games, complete absence of a midfield etc. I just don't think Eddie has an answer, and he gets found out by tactically braver/more astute managers time and time again.