Why is Sedevacantism false?

Vatican II appears to me to have been a schizophrenic episode in the life of the Church. With the psychosis still going on and getting more intense with Pope Francis. It’s as though there was a Spirit of Vatican I that has been replaced with a Spirit of Vatican II. Or as though the latter council was a counter catechism to the former. It’s extremely hard to interpret Vatican II and what came after it with a hermeneutic of continuity. I would love examples of this being done with the most controversial of the passages in that council’s documents. I have been looking at a lot of Sedevacantist material, especially that of Most Holy Family Monastery, and what it says seems to make a lot of sense. All they seem to do really is take the infallible statements of the Popes and Ecumenical Councils seriously, as well as that of the Magisterium. And there have certainly been more than two ex-cathedra statements from the popes, contrary to popular opinion. Long before Vatican II, both Communists and Freemasons openly declared their intention to set one of their own on the throne of Saint Peter. They were once very powerful forces in society, and probably still remain very influential today. Prophecies abound about a Great Apostasy that’s supposed to take place. And the Third Secret of Fatima was supposed to be revealed no later than 1960. Something just doesn’t add up, or rather, something does seem to add up, or at least appears to. I don’t believe anyone of good will can read the writings of the Church before Vatican II, compare them with that council and the writings after, and say everything is fine and dandy. Therefore my question is to those who recognize that there is at least a major crisis in the Church, why is sedevacantism false?