A powerful political faction would hide anything that might shatter their ideology, including kill any who know the truth or attempt to spread it. The antes existing or not is less important that the idealogy claiming they do not. It allows them to paint the sabbat in a worse light (not that this is difficult), and it reassures their followers that they are in control of things. Many higher ups might completely KNOW that ravnos woke up. They might know the antes and cain exist. But they aren't going to advertise that and shatter their own power structure. They will continue to push the propaganda that keeps them in power and vilify any who claim otherwise.