Thank you for your comment.

Steem is a Decentralized blockchain and a Social media Blockchain, I think the secrecy of the mimblewimble protocol goes against these purposes.

Steem as a Blockchain can adopt the MimbleWimble protocol and transactions are done on the steem Blockchain like any other Blockchain. Somebody can transact on the steem Blockchain without using the social media aspect of it and will require more privacy in terms of his address, receivers address and quantity of the token sent and may require such privacies which is the aim of the MimbleWimble protocol.

Hope you get the gist?