Since the moon was formed 4.5 billion years ago it has been moving away from earth 1.6 to 4 centimeters per year. The moon is the perfect distance to appear in the sky the same size as the sun and block it out. The more the years go by the more the moon will be moving from the Earth.
When the Moon first formed around our Earth over 4 billion years ago, it was much closer to the Earth and appeared much larger in our sky. So total solar eclipses in the early epochs of our Earth did block the Sun but also most of the corona. Over the eons, the Moon is gradually receding from the Earth due to the friction from the tides.
The last time the contiguous U.S. saw a total eclipse was in 1979. That was 38 years ago. On August 21 we will get the chance to see the solar eclipse.