It makes perfect sense to me. If I were running a MSC and a shopper deactivated herself, I would believe that the shopper no longer was available to work for my company. After all, if a MSC deactivates a shopper, what is the shopper's perception? Would the shopper believe it was a temporary deactivation that might be reversed at any time?
Maybe you will be able to explain and get them to reactivate you. Or, perhaps you can reapply.