Maybe the answer is more obvious than I think, but I don’t know how to explain it.
It seems like since at least the 1990s (if not the late 1980s) the default antagonists in realistic, contemporary settings have not been governments or nation‐states, but foreign terrorists. You can find this trope in almost anything modernistic, from 24 to Bad Boys to Call of Duty sequels to the Diehard series to James Bond sequels to obscurities like Nuclear Strike to the Soldier of Fortune series to Syphon Filter to Lady‐only‐knows how many Tom Clancy books/films/games/shows/songs/baseball cards. Hardly anybody seems to find anything weird about this.
What is so fascinating about foreign terrorists?
I think it’s just lazy writing. You need bad guys for the story and terrorists fill that criteria well enough.
“Fighting terrorism” is also the usual pretext for US aggression, so the years of propaganda might have affected the way people think about the bad guys trope.