The majority of lavabit users probably joined on principle and would not be harmed by the NSA having their secrets at present. For those users the convenience of getting hold of all their mail (if they didn't have a local backup) might be worth the tradeoff of having to change their password and risk the NSA recording/decrypting their data on lavabit. Others could simply not access the data if they want to leave it encrypted.

At least this option gives the users that choice.