My guess is an increased focus on team defense has made that a top priority in players minds, which is actually kind of working to improve the d but everything comes at the expense of something else, in this case it’s offense.
Beyond that, I think it’s a bit of luck that is snowballing into confidence issues. Mika starts sick and out of it, Chytil misses a ton of time, Kakko is in and out, Panarin is gone for weeks, the defense is a revolving door of injuries for a while. It’s a lot for a young team trying to find their way even in smooth circumstances. And on top of that a lack of ability to adjust the gameplan on the fly midseason by the coach. And a continuation of as easy going “well get em next time” attitude.
First thing to try is a new, more experienced coach imo. I appreciate not keeping this coach recycling thing going and I don’t think Quinn was a terrible hire for a time, but something fundamentally has to change here and the coach is by far the easiest and maybe most important single change. The thing is I don’t see this organization just firing their guy and throwing in an interim or something, they’ll want a new “their guy” to replace him and I don’t really think that guy is available right now