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Any idea how much SBD was stolen last year?

No, this can't be read from the blockchain data. It is only transferred from one account to another. The data doesn't show whether the recipient is a fraudster.

why SBD is not protected unlike the savings and SP

Firstly, the coins are protected by keeping the keys secret. If nobody but the owner knows the keys, the coins cannot be transferred.
SBDs are similar to STEEMs. The owner can keep them liquid or transfer them to the savings (SBD and STEEM). What would be the alternative to liquid SBD/STEEM? A transfer that takes a day or even longer? Every system architecture has to find a compromise between security and usability. I think there are already a few more securities on the Steem than on other chains (recovery).