Bitcoin right now is not really anonymous. Monitoring the unencrypted peer-to-peer network, analyzing the public blockchain or Know Your Customer (KYC) policies and Anti-Money Laundering (AML) regulations can reveal a lot about who is using Bitcoin and for what.
This is not great from a privacy perspective. For example, Bitcoin users might not necessarily want the world to know where they spend their money, what they earn or how much they own; similarly, businesses may not want to leak transaction details to competitors.
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https://bitcoinmagazine.com/articles/with-tumblebit-bitcoin-mixing-may-have-found-its-winning-answer-1477423607
