The reason why BTS members have to join the army is because of South Korea's conscription law. It's a law that requires all men to serve in the military to protect their country. It's kind of like how Spider-Man has to save the world, but instead, it's more like real-life superheroes protecting their nation.
Now, you might be wondering what happens to BTS while their members are serving in the army. Will they disband? Will they stop making music? The answer is no way! The group will just go on hiatus, which means they'll take a break and come back stronger than ever, just like Baywatch lifeguards saving the day.
So, which BTS member is next in line to join the army? Well, it's likely to be J-Hope, RM, or Suga, as they're all around the same age as Jin. But, we'll just have to wait and see, just like waiting for the next episode of our favorite TV show.
Jimin & Jung Kook Finish Military Service as BTS Reunion Approaches