Number one reason why BTS is different from other K-pop idols is that they did not limit themselves to just their country or the Asian continent. They extend their wings and also target the United States market. Their rap and pop style of music is more acceptable in the US than in many other countries. The number 2 reason is that the BTS guys are extra talented. They are really good at what they do, and they have all the skills required to independently standout.
The third reason is simply that the BTS members have a great synergy effect. They distribute roles among themselves, and they perform the roles efficiently and effectively. The fourth reason is the topnotch quality of their music. They do songs that range from hip-hop, rocking dance, EDM, trending pop, and several genres. The fifth reason is that BTS does not just write lyrics on love, beauty, and party like other K-pop idols, but their music usually connotes a story on reasonable and social topics.