Were all the address were used? If not then walletexplorer won't link. I think walletexplorer only links addresses when a certain addresses links and sends bitcoins to the recipent's address like this:
Of course 
Addresses are unknown until they are used, that's just part of the Bitcoin design.It would be impossible to list unused addresses, as it's very easy to create billions of them.
I'm not entirely sure how Wallet Explorer links addresses together. They must heavily rely on address reuse, especially online services often use the same deposit address.