It's probably because they've lost most of their fans, and of the ones who are left, the ones who spend the most money by far are the freaks who buy 20 copies of every PB, go to every concert, and essentially live with the fantasy that the girls belong to them. Those freaks are UFA's bread-and-butter. To satisfy them, Yaguchi could easily be sacrificed. She was probably making way more than the youngsters anyway, and UFA could see it as an easy cost-cutting measure.
Or it could be that she was offered the opportunity to recant and stop seeing Shun publicly and she refused. Maybe UFA, said, "You disobedient child, we're gonna put you on punishment just like we did with Nacchi," and Mari said, "Oh, ya think? Well fuck alla y'all, I'm outta here."
heheh. It would be cool if she said that, but I'm talking out of my ass, obviously.
