BTS' biggest rival was EXO, but its many issues helped BTS to reach the top.
But, Seventeen was creeping up from behind, and although BTS was more popular outside of Korea, SVT had more exposure.
Plus, SVT had a Chinese member, which gave a good boost in China as well.
As SVT showed the potential to be BTS' rival, trying to stop BTS's tracks, Hitman Bang Shihyuk made a masterstroke - he bought Pledis, SVT's company, and made sure SVT would never overcome BTS.
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I am in the school that rivalries in KPop is just time consuming, energy depleting exercise which lead to no good outcome.
GFriend menacing Twice's way led Twice fall short of its ambitions.
The many rivalries in KPop, like Wonder Girls - SNSD, BTS-EXO and Twice-BlackPink ended only when one side became too exhausted to continue the rivalry, and because BTS spent so many years fighting EXO, it is in its 9th year and only after they had shaken off the last of their rivals they could advance.
If SVT had continued to be a thorn at the side, BTS would have to deal with them sooner or later, and Hitman Bang buying Pledis ended that.
SVT debuted in 2015, and it didn't really owe too much to Pledis, but because of the contracts it no longer has any possibility of threatening BTS. Hitman Bang understood that rivals only sap your energy.