Kpop has been and always will be niche. Marketing will help expand that niche but i doubt Kpop will ever be mainstream. First is racism, nobody wants to see Asian singers/performers for some reason, the only true superstars arent really coded Asian (nobody knows that Bruno and Olivia are half Filipino, everyone thinks theyre latin if anything). Secondly, the language barrier, only 1M speak Korean in the US in comparison to 50M Spanish speakers which is why Spanish songs have a much easier time charting here. Thirdly, the genre, Kpop is boyband music, which has never gotten respect, it's always been relegated to the realm of adolescent teen girls fangirling over hot young guys, nobody considers Backstreet Boys, Nsync, 1D as true artists just manufactured industry drones.
This is ok though. Kpop doesnt need to be like hip hop or RnB. There is plenty of money to be made along the edges of the US mainstream, even just 2-3 percent of the US music market would be a ginormous boon to most Kpop groups.