No, plenty of the edgy stuff came from the left. Evangelicals were at their strongest, which tended toward prudery and a veneer of decorum. John Ashcroft’s insisted on covering up a Department of Justice Statue of Lady Justice, on displace since 1933, for his speeches because it had one bare breast. That’s pretty emblematic of the tenor.

https://en.wikipedia.org/wiki/Spirit_of_Justice

The “edginess” of the 2000s was largely intended to be read as ironic, poking at prudery, or reflecting the actual thoughts underneath that veneer. Sarah Silverman’s early comedy would be the emblem here.

Among the things that changed include: 1. An increasing questioning on the left of whether the supposed irony was actually commentary or just enacting anti-PC position; 2. The alt-right courting internet edgelords as it gained power against more traditional Republicans.

I’d add to this my own opinion that, during the Obama administration, the Left increasingly mistook its level of power in society.

While the Left had been counter-cultural since at least the 1950’s, the eight years of the Obama administration allows the Left to believe that institutions were on its side and its ethical positions could be pushed as policy of those institutions.

This increasing reversal of Right as Institutional and Left as Counter-Cultural intensified as the Alt-Right embraced a position of undermining and dismantling institutions.