Without the consoling views of the future, the Jewish people would have given up long ago. Now, G-d wants many different types of people in this world. Some people are gifted with talents of charisma and verbal persuasion. Also, Man's free-will must be maintained up to at least the time of the Messianic period. So, people must be able to use their talents to do good or bad.
People are even free to talk themselves into believing that a bad thing is good.
Throughout history a lot of people have really have wanted the Messiah to come already. It's a huge market. The potential therefore exists for either well-meaning or corrupted people to exploit large masses of the population with false Messianic schemes. In His genius, G-d specifies in the Torah what the Messiah must do. Promises or claims won't work.