Reasons likely are:
Bit Blender: Hhampuz actually was able to make contact with blender in the forum (or even beyond the forum) to send rest of unused fund back.
Thank you very much Campaign Manager Hhampuz!
Everyone should have been paid and Hhampuz sent me the remaining coins.
Best Mixer: their site suddenly seized and there is no way to contact with them. So, how to send rest fund back to Best Mixer?
I've never had any contact with BestMixer outside of this forum, the account that messaged me never even gave me a name at the bottom of their message. I once asked if we could talk outside of bitcointalk since it would be easier and due to them not being online here that much. They declined and said this will be the only form of communication.
If Hhampuz actually sent unused fund back to Bit Blender (long before the accusation), I believe the only reason that he has not made the same thing for Best Mixer is unable to contact Best Mixer team after all. The
bestmixer account was last actively on 19/5/2019, long ago before the bestmixer shutdown.