It's no secret that Kiara has a strong bias towards her female fans over her male ones. In fact, she has frequently lamented the fact that she does not have more cute girls in her audience.
Wanna know the best way she can acquire more female fans? By collabing with HolostarsEN. You can see proof of this working in Nijisanji, where the girls used to have an almost entirely male fanbase, but have attracted more women since associating with the males (they frequently share their analytics and talk about the changes). The number of cosplays they've gotten has shot up exponentially as well. If Kiara wants more girls to watch her, this is actually her golden opportunity. She may not like or care about StarsEN at all, but, from a purely pragmatic stance, she would be stupid to avoid collabing with them.

tl;dr: Pander to unicorns, get a fanbase of unattractive loser males. Collab with the stars, get some cute girls to watch you.