That's a good reason. But even if they speak up and law enforcement agent arrest them, is there a means to prove that they are the real owners of the fund. I mean from the chipmixer data base.
Proof of addresses that sent the funds to the chipmixer deposit addresses
Meanwhile, I don't think that anyone is in active use of the chipmixer site because the backend is still with chipmixer, what was seized was just the front end.
I am not sure if I read right what you said, but for your information, Chipmixer was never a decentralized it service. It was centralized and the Law enforcement chaps got a hold of some of their servers and lots of data according to their report.
And nope, the backend must have also been seized, otherwise how do you explain Law enforcement draining people's Bitcoin like in OP's case?