Nijisanji managed to shoot themselves not just in the foot, but in the head several times. It was a great display of incompetence on their part and a much better example of a company run chasing shareholders than this one. I imagine Cover's problem is that some of the girls probably had cooled off and became more lukewarm on the company, some had legitimate health reasons to leave, and their management pushed a rather minor internal change that made those girls decide they wanted to bow out while the ones who had more reason to stay shrugged it off.