Well, you do play in a killer conference.
From where I'm sitting, your low defense rating did you in. Speed opens a lot of doors in this game, but a low-30s defense is well down there. Combined with the fact your press IQs look like they may have been in the B+ range for a chunk of the season and that leads to your high foul count, the fact your opponents outscored you by 200+ points at the free throw line and averaged better than 30 foul shots a game and how they almost matched you in FG and 3-pt percentage.
In a "normal" conference, this team dominates (thus your non-conference success). In an elite league where pretty much everyone is in the upper echelon for team athleticism and speed, they were able to exploit the defense rating. Your athleticism isn't bad, although for running a press it is a smidge below where I'd want it to be, but I don't think it's so low that it really crippled you. The defense number though definitely hurt. I didn't peek through all the losses, but I can definitely see, given the strength of the conference, how this team finished where it did in league play.
Also, don't know when the starting point of your "what has changed since" title is, but if you're not aware, they dialed back the 3-point effectiveness a few months back, so if you're coming back into the game and your previous experience was, say, a year ago, be cognizant of the fact that high-perimeter players aren't knocking down the outside shot like they once did (the change was made to bring 3-pt percentages back in line with the "real world"...or so the explanation at the time went)