Problem with adding anonymizing wallets and mixers to bitcoin is that they can never be as good as a coin that natively supports anonymization. And I think it's safe to say by now that bitcoin isn't going to change their protocol to add new features - they will at most fix issues only when absolutely necessary.

Bitcoin mixers and web wallets can be honeypots just waiting for people to use them - it must be guaranteed in the coin's native protocol without any 3rd parties that the privacy will be retained. And even if you could trust the 3rd parties, it will be super easy to make a mistake that will reveal your activities - and if it is possible to make a mistake, believe me, people will make them.