User blog comment:Angel Emfrbl/Well its definitely official/@comment-26116982-20150518012902/@comment-53539-20150518110732

I made a mistake myself with One on the first day, because I didn't expect the change to CeVIO.

My guesses
 * because CeVIO right now is just establishing itself so their hopping on board early.
 * The producer base for CeVIO thanks to its free version hit 300,000 downloads for a new software alone. This pales any voicebank released for Vocaloid when it was that young.
 * Cheaper licensing?
 * Not putting all their eggs in one basket?

I've got more but their the 4 I felt were most obivous.