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?
Pop culture derives from larger material forces at play and seeks to legitimize and reinforce those. The US is at war with X, therefore media naturally follows and portrays the enemy as some variation of X. Some of it is manufactured consciously (MoD obviously), some of it is just financial incentives. People are interested in current thing, naturally want their media to “wrestle” with current thing and tend to consume media “wrestling” with current thing, so companies pump that stuff out because it sells.
There’s nothing inherently fascinating about terrorists, that was just the current thing for the last 2 decades and therefore created attention, because it felt relevant. It also constantly created and reinforced an easy good-bad dichotomy of the conflicts those narratives were based on and that’s nice too.
Just watch the terrorist antagonist fade away and producers moving to the Russian threat again.