BTS got big because of their close, active relationship with their fanbase that they did better than other groups at the time. And they had a style that Americans and other Western folks liked.
Same for BP: their songs and their style, their whole image is to the liking of Western peeps. More so than with most other groups.
That YG has a knack for creating an image for his groups that appeals most to especially Americans and Western folks, he already proved with 2NE1 and Big Bang. And Teddy is the one that can consistently (but not regularly) produce the sound that goes well along with it.
Why other groups even of Bighit and YG themselves can't reproduce this success is a different puzzle though.