Quoted By:
Because they are women.
But I guess also Nina is a big "grab the nearest cock and leech" afficionado while Pomu likes to hang with Shu and Doppio and Luca but will keep them at arm's length to not upset her gachis. In a way both of them are obviously cunning whores, but Nina probably dislikes that Pomu grooms her chat while pretending to be 'seiso' while she also knows Pomu thinks idols tending to keep relationships a secret or not date at all during the 5-10 years between the ages of 14 and 24 when women tend to be in idol groups in order to not upset their fans is stupid and gay, so Pomu's seiso is fakeso ie not something she genuinely believes. Pomu herself was probably a 'victim' of Nina, since Nina obviously is more aggressive/moved first, but Pomu has more group pull being friends with lots of the girls.
Though there's also other stuff like Ethyria being full of bitches, but REM want to lose their religion (believe in iinari-ookami-sama the kitsune god in nipland) and avoided Nina early on because she was a cunt to them.
So I guess it loops back to "because they're women".
