They play the same songs in the US, nb
BTS didn't make US-specific songs
That's exactly why the whole thing is important: they did the breakthrough singing in Korean, with their own songs, not produced by American producers for an American market, but written by themselves, primarily for the Korean market.
I think their success in korea and worldwide is attributed to many things, their looks, their insanely good choreographies, also the music (hey, these are good songs!), the whole stage they do, and because they are humble and funny and nice guys on camera. The package is just bombastic. There are bands who have more members (Super jUnior had 13, and there's some band with 17 members...), so I don't think it's because they are 7 and not just regular 5 members
The package is appealing, they are also young and in the right age for teen girls. Of course, they needed to be lucky, too, be at the right place at the right time. There were other Korean bands who were prominent on US charts before, like Bigbang. But Bigbang is now in the military and currently, quality-wise BTS is really on top.
I think fans must not forget that BTS' way was paved out by earlier bands who were pounding on the doors of Western pop culture, and made it easier for younger bands to go further. Bigbang filled the London O2 twice as early as 2012, and toured US
arenas, all sold out. They still keep the record of the biggest world tour in Kpop history with 1.5 million attendees. This will likely be topped now by BTS, but still....
It's not out of the blue that this is happening. The road has been paved.
I'm an avid researcher of Kpop history and it is fascinating to see the events in the light of the past happenings.