Well, I wouldn't use the word "advanced," in the first case or "less advanced" in the second. For the past, I'd say "(largely needlessly) over-complicated." And, at least in the field I know best, the field of literary criticism, the same guy who's part of the blowback, Greenblatt, was the discipline leader back in the day (though even then he was less obscurantist than most). Now, he and others like him will have a second reason for bothering to write for a general audience. They believe literature and literary criticism should be agents of political change. And they got to thinking, "Hey, if no one can understand our stuff, how is it going to make any difference?"
The OP (and remember, this is a resurrected thread) was lamenting that scholars who had previously been more advanced were now writing less advanced books. I'm sure it's for all the reasons given. But some of these people have won all the renown they'll ever need in their disciplinary circles, and can now afford to reach out to the hoi polloi.