Why Oval? Who knows. But it is considered the ideal. Aesthetically pleasing to the eye.
We know of course that there are lots of non-idea face shapes that are beautiful, but for those who want to aim to be as close as possible to the ideal, read on.
Take the humble egg and flip it vertically and you have close to the idea face shape.
Once you know your face shape, you can utilize makeup - contour, highlighter, blush - and hairstyles to balance things out a little. Face shapes also are a factor in the types of necklines, jewelry, and other accessories you can wear successfully.