The too long, didn't watch version:

1. Americans, particularly the right-wing, took 9/11 very seriously- to the point that anyone who was against war/American military expansionism in general and Iraq/Afghanistan in particular, were branded as equivalent to the terrorists who flew the planes.

2. The rise of flag-waving bro-country America uber alles nationalism which more or less flooded the airwaves.

3. The difference in the origin of the conflict. Even though both conflicts had a sense of "doing one's patriotic duty" and a pervasive view that opposition to military intervention was unAmerican, the fact that the public had a clear perception (accurate or not) as to why we intervened in the Middle East meant that opposing views had a harder time getting mainstream traction. By contrast, no one knew why America was in Vietnam- so even though you were expected to "support the troops" and go if you got drafted, war opponents could safely point to the muddy origins as a solid basis for their views.

4. Finally, the widespread nihilism among GenX and Millenials. Everything sucks, nothing is going to get better, so just fuck it all.

Smash all of that together, and what you're left with is a music scene that's full of either "If you don't literally fuck this flag right now you're a dirty Muslim terrorist!" or milquetoast "Hey W sucks and war is bad but the troops are kinda okay we guess"

Until, of course, Green Day.