Also wing leading edges and all other subsonic streamlined bodies have a rounded front. It gives the lowest drag.
Here comes in very, very layman's term a few lines about a subject which fills hundreds of books.
A body traveling through the air sends a "warning" forward telling "here I come". That warning travels at sonic speed since it is in fact the same air pressure disturbance as sound is.
When traveling at supersonic speed, then the body always flies ahead of the warning. Therefore entirely different physical laws apply, and the body virtually has to slice its way through the air as a knife.
But go to the public library and borrow one of those books, the thicker the better.
The Space Shuttle (and all other re-entry vehicles including warheads on intercontinental ballistic missiles) are different animals. Internal heat distribution is more important than lowest possible drag, because a pointed nose would always burn away. Therefore the rounded shape.
Always keep your number of landings equal to your number of take-offs