Porphyry’s Explanation of his Lameness

“Again, the power of fire they called Hephaestus, and have made his image in the form of a man, but put on it a blue cap as a symbol of the revolution of the heavens, because the archetypal and purest form of fire is there. But the fire brought down from heaven to earth is less intense, and wants the strengthening and support which is found in matter: wherefore he is lame, as needing matter to support him.” – Images, Fragment 8

 
So, Hera being the Queen of Heaven, conceived a ‘weaker’ fire and chucked him down to the earth.