Probably because they were always often promoted as more artists than idols and they were also from a small company. It was also hard for them to stand out w/ SNSD, 2NE1, Wonder Girls, T-Ara, f(x), Kara, 4Minute, Sistar, etc. in the mix.
I believe they're underappreciated for sure. Miryo is arguably the greatest female rapper of any generation (she was a member of the collective Honey Family) and JeA is also one of the best singers of her time. Gain also had some good solo hits (such as Bloom) and Narsha frequently appeared in variety shows.
