Yeah, every politician really doubled down on flag pins after 9/11. It never really went away. Almost all of them do it or are afraid of being called unamerican if they don’t do it.
Obama went without one a single time in the 2008 campaign and got lambasted for it. It was never a thing before 9/11, but now it's just another bit the flag waving crayon eaters of the Republican party can use to pretend they're the only patriots.