That's got to be rough for the J-pop industry. For 20 years you foster a passionate niche following in the West, and just when you think you will break through, South Korea runs up and steals your lunch.
At least Japan still has a stronghold on Manga and anime! Even though I dont watch that stuff.
And that is where J-pop went wrong. The Western J-pop fandom was synonymous with the weeb subculture, so it came with a lot of baggage. K-pop made it to where it was in the West on its own merits. Anime made people into fans of J-pop. K-pop made people into fans of Korean pop culture (manhwa, food, fashion, K-dramas).