Personally I appreciate why smart bitmixer's owner was, this person is great. He created the most amazing mixer and also he closed it himself. To make it more clear, only in 2015 year bitmixer was roughly mixing up to 60K-70K coins monthly (they launched service in 2014 year). Then in 2016, bitmixer owner stated himself that their website mixed 1 million coin. So what do you think, how many people were using it for just protecting their privacy during online shopping? I think maybe some percent only, max 4-5%. See how many websites were seized and how many still aren't and how many things are done without websites via different messengers.
Nowadays mixers aren't used for good purposes, it may was in 2014-2015 year just for the interest of mixer.