Tbh, I believe a lot of different parties are at "fault" here - Levy, AVB, bad luck with injuries, Miss VdV's illness and Modric's understandable hankering for better things, our scouting team, Porto, reality (in terms of the fact our rivals can outspend us by hundreds of millions), and our own boo-happy fans. There's no single reason - everything adds up into a feedback cycle that magnifies and reinforces our issues.
In truth, I think the fundamental problem still goes back to our mutilated squad, and that goes back to money (= our small stadium, or Joe Lewis not being a sugardaddy). Iirc it was Soccernomics that showed an incredible correlation between wages and finishing position in the league, and we have the sixth highest wages at best, while trying to squeeze into a tier of rivals who have *substantially* more money than us. Even on paper, I don't think we have any better than a midtable squad this year because we are so lacking in crucial qualities - not just creativity and vision and intelligence, but the basic ability to keep the ball under pressure, and to press ourselves (which I am definitely looking at AVB for).
Now, could we have backed up AVB better in the summer window? I think so, if we had not spent on both Dempsey and Sig (one is enough, thanks) and instead put that money into the one player AVB was desperate for - but then again, who knows what shenanigans Porto was up to at the last minute? So it's hard for me to blame Levy entirely. He is working within severe limitations - realistically we can't afford long-term salaries on the level of Bale and Ade, esp without CL, and still splash record transfer fees, but we have to pay that anyways or lose them to reality and risk a fan riot. Football as a sport is like a runaway hamster wheel - you have to pay more and more just to stay in the same position, so every year it gets harder and harder to compete.
At the same time, we ought to have enough talent and money to be outplaying, or at least controlling the game, against the likes of Norwich and Wigan. Here is where AVB needs to earn his dough. I don't need to see some brilliant swagger from a team that really doesn't have much, certainly not consistently, but I think even the most talentless donkeys (which we are not) can show much higher workrate and some actual pressing and composure on the ball ... at least as much as Wigan or Swansea. AVB has compounded the problem by not starting Ade and Lloris, while the loss of our five highest passers from last season - BAE, Parker, and Ade to injury/selection, and Modric and VdV to other teams - has deprived us of players who are actually interested in the ball and who might touch it more than ten times a game.
To that end, I'm also pointing to Everton as an example that you can still find talent even without much money if you have the right scouts, and to Swansea as an example that you don't necessarily need the most talented players to still control midfield. So ... our scouts. What the fudge are they doing? Yeah, ok, the money thing sucks, but we're not totally helpless here. If we're going to compete we need maximum concentration and commitment from everyone in our squad, a better go at things from AVB and Levy, and more creative scouts and a better youth system (which tbf, we are working on).
And finally, the fans. Seriously, I know we're frustrating to watch but we're not helping things here if we're booing our own club. When the going gets tough we ought to be more supportive, not less. Because our team needs us right now. And yet - I can understand the frustration of someone who pays a ridiculous amount of his or her hard-earned money to watch these turgid displays every week. It's not ideal, but to me it's understandable, and it goes back to the reality of football as a rigged game, a hamster wheel spinning itself off the brink to oblivion, demanding more and more blood to feed itself. Maybe when the bubble bursts, our connection to football will come back. For now, I think we have to ride out the ugly transition period.