The reaction of benzene with excess of chlorine in the presence of sunlight produces 1,2,3,4,5,6-hexachlorocyclohexane as the major product. This is also given in the preparation section of the Wikipedia page on lindane.
Also, multiple chlorination of methane is also well-known, specially when chlorine is in excess. For example, it is mentioned at the bottom of this page from MasterOrganicChemistry.
My question: After hexachlorocyclohexane (lindane) is formed, I thought that it is an ordinary haloalkane, comparable to chloromethane, so if chlorine is excess, it should also substitute the remaining six hydrogen atoms from lindane - forming 1,1,2,2,3,3,4,4,5,5,6,6-dodecachlorocyclohexane. Since the reaction is used industrially, what I propose obviously doesn't occur. Why is that so?