I think most non-native Koreans or people who don't speak Korean like the fact that they can't understand the lyrics. I know that was one of the draws for me when I was younger -- I can't understand it so the voices just become one more instrument at play. Sometimes lyrics can take you out of a song, after all, when it's bad or cringe or just plain stupid.
HOWEVER, as I am today, and as I see music as universal, and as I still do not speak/understand Korean, I just don't care to see it as selling out. And I also consider this -- there are a lot of Korean POP songs are not penned by Koreans. I also consider this -- that a lot of popular songs penned by Koreans/produced by Koreans, like with any other person involved in the music industry globally (I'm not wording this right, but basically American, Japanese, Chinese, European, South American, Hispanic, etc.), rides the trends both nationally and internationally. They want what's hot and what's going to sell.
So, just as I'm not gonna call a K-group a sell out for having someone like Teddy Riley pen their lyrics (because even if they translate the majority to Korean, at it's core it's written by a non-Korean and produced to reflect a sound that's popular/derived from African-American R&B), I'm not gonna immediately think "sell out" when I hear a Korean group produce English songs. I never thought it years ago when Miyavi crossed over and I don't think it now when BTS/BP/MX/etc. do the same.