The thing is they can't remove them because
1) Qri's fans including those ahjussi(s) will storm into CCS's building and create some mess
2) Qri's fans will be joined by Boram's father with some very influential people from the industry behind him. This will definitely turn CCM's building upside down
3) There will be no suitable 'candidates' to sing those 'yeah, yeah', 'oh uh' lines anymore cause basically Qri and Boram have been doing this for a very long time which means they are already expert in singing those lines?
To be honest, although Qri and Boram's singing lines are next to non-existence but they are still important in T-ARA in my opinion. For instance, I appreciate Qri and Boram's singing in cute songs like O My God. I don't think anybody in the group can sing in a cute manner as the both of them. In Cry Cry, besides Hyomin's stick and Jiyeon's "deep in your eyes", the next thing that attracts me in their live performance is Qri's "Hey T-ARA" (opening) and her "SHHHHH !! T-ARA, time to love" (closing). For me she absolutely killed it with that SHHH !!! T-ARA, time to love as their closing line.
Talking about visual, Qri serves as one of the visuals of the group. Her image as the ice cold princess who doesn't talk a lot gives me a mysterious vibe which makes me want to know more about her (I watch Pretty Boy for T-ara). Although Boram serves as the visual of the group in a different way and to a lesser degree compared to Qri, Boram is super cute for her age and not to mention when you see 7 people on stage and there's one short little girl look-alike, people go, "Oh, that's T-ARA because there's the shortest member of the group".