How come God reveals Himself to some people and to others he does not? Because it is God who chooses and not man. In the first reading, God chose Moses to receive the Ten Commandments on Mt. Sinai and not any of the other Israelites. He chose Israel to be his covenanted people, not because Israel was a great nation; he chose Israel because he loved them.
In the Gospel reading, Jesus reveals the mysteries of the kingdom of heaven to his disciples and not to the crowd coming to see him everyday. Why only to some, and not to all? God always chooses a select few because his teachings are sacred and not to be given to just any curious onlooker. He also chooses the humble ones, those who are weak and nobodies in men’s eyes, in order to confound the proud and the powerful. The choice of God is his and his alone. What we can do is to heed his call to follow him if and when he calls us.