Why do so many people believe this man?

They are following a false prophet. God has warned many times in the bible against false teachers and prophets, and he's one of them. He is just one of many false prophets who will lead people to the slaughter. Only God alone knows the day, the season, the time, and the year the world will end. Jesus says it is not for us to know. We'll find out soon enough as the End Times approach. There will be signs here and there that we're close, but it doesn't signal the end yet. It is just the beginning of sorrows to come.