So some group may have advantage for using this kind of service
Bitcoin isn't anonymous at all, and especially not when it comes to the majority of the people. In most cases people buy their first coins from an exchange, where in current times account verification is a must, so all the coins they withdraw from that exchange, will have their personal information attached to them. In order to get rid of that personal taint, people mix their coins. It's as simple as that. Bitcoin is no longer the preferred way of settling illegal transactions, where I have been seeing privacy centric coins as Monero gain more popularity. I am just waiting for the day these privacy based currencies start being the main currency on dark net markets -- the sooner that happens, the sooner we get rid of the idiots blaming Bitcoin for everything that happens.
Can somebody answer why bitmixer closed anyways?