Why is image formed in front of Retina in a myopic eye, not behind it?

In the normal cases, image of an object is formed on retina.

Elongation of eye ball causes image of an object to be formed in front of the retina and the focal length of the lens decreases.

To see a distant object clearly, the focal length of the lens should be larger. So, a person suffering from myopia is unable to see the distant objects clearly. In this way, elongation of eye ball causes myopia.