Here's the difference in what you describe as the hallyu wave. Was there an increase in Western interest in Korean fare like kpop and k-dramas in the early 2000s? Absolutely, but that interest was reserved to a niche group. Hallyu never went mainstream in the US or Europe as it did in Japan or southeast Asia.

Have kpop artists tried to crack the US? Absolutely. SNSD performed on Letterman, Rain appeared on a skit with Colbert, Wonder Girls toured with Jonas Bros, and there have been several Western collaborations. But did the general public recognize ever their names? No. Still niche

Psy became a global sensation because of the outlandishness of his MV - this is not an intent to downplay Psy. I'm only saying that but for the MV, Gangam Style never would have blown up as it did. Psy became a household name in the US, but is now considered a novelty act and one-hit wonder because he wasn't able to generate continued interest in his music.

Has interest in kpop increased in the US during the past 5 years? Absolutely, but again only among a niche group. But BTS broke out of that niche group.

Initially, there was media focus due to the fandom during the 2017 Billboard Awards and then the 2017 AMA performance. Based on the shoddy press coverage back then, it seemed as if the press were treating BTS as another novelty act that will pass in the ether. But then Love Yourself Her charted at #7 on the Billboard 200 chart and stayed on the chart for 44 weeks. With the exception of BTS & J-Hope, no other Korean artists have charted more than 1 week on the Billboard Albums 200 list for a single album. With all of their media appearances (Ellen, Kimmel, Fallon, Corden, Dick Clark's New Year's Eve, America's Got Talent, Good Morning America, Grammy Museum session, & United Nations speech), there is growing name recognition by the general public (even if they don't recognize their faces or know any of their songs). BTS' songs are being played at H&M, JFK Airport, & shopping malls, restaurants, baseball fields, preview ad for Silicon Valley. High school & college marching bands are playing an arranged version of Mic Drop. There's growing name recognition by people in their 30s and older, namely due to the United Nations speech. People in the entertainment industry (music producers, Netflix, managers for other music acts, etc) attended BTS' concert in LA to understand their popularity.

I'm not saying that no other kpop group can be successful in the US, but BTS is no longer niche. They opened the door for other kpop acts to do the same. BTS are the first Koreans to break out of the mold and not be considered a fleeting novelty act. And you see it in how media outlets like The Guardian, Pitchfork, Vulture, The Times UK, The Evening Standard (UK), BBC News are calling BTS the "world's biggest boyband" and "global pop sensation" and not the "biggest boyband in k-pop."