Why do crystalline solids have definite heat of fusion whereas amorphous do not?

Crystalline solids have same properties in all direction of the crystal, they have a regular and repetitive arrangement of constituent particles, and thus a sharp melting point. They do not flow before melting. Hence, they have definite heat of fusion.

Whereas, amorphous solids do not have a regular pattern of constituent particles and thus do not have a sharp melting point. They melt over a range of temperature and start to flow without completely changing into liquid. Hence, they do not have definite heat of fusion.