They could certainly petition the government for the return of money that couldn't be tied to anything illegal. But is the potential demand of return of money a hindrance for the government to auction of the Bitcoins? If anyone demands their money back, and the government agrees, or is forced by a court to pay it back, they can do so without holding BTC in the meantime.

Presumably they've made an assessment and come to the conclusion that either the percentage of assets held that belong to customers of SR that said customer may have a claim to is small enough that it's easier/cheaper to deal with that if/when anyone makes a demand than trying to sort it out before auctioning off the BTC.

Especially given that presumably very few customers of SR have only bought/sold legal goods, and so presumably most of them won't want to identify themselves.