To be honest, I thought it was a standard not to require an account before someone used a mixer. This is the first time I hear that some mixers actually require their users to sign up. I haven't seen one yet. Even if there was, I did not notice or did not use them.
Previously, there were various reasons why some mixers went in the direction that users should have accounts with them for the mixing process. For example, whirlwind.money also offered a staking option, because the funds would still be used for the mixing process, but that didn't end well. However, we do not know the exact reasons for closing this mixer.
However, over time it has become clear that mixers must have as high a level of anonymity as possible, and any collection of data, even if it is just a username/password, does not support the basic purpose of coin mixing.