Just guessing. It is possible some MM in such cases are also looking at criminal sanctions, but any criminal investigation would be publicly undisclosed for obvious reasons, but at some point suspects would be alerted and start to lawyer up on that front. My memory from old news articles, which could be faulty, is that sometimes criminal investigations get resolved or satiated by the authorities seeing civil settlements with the victims — (aka: the wrongdoers recognizing and remedying the error of their ways.)
The biggest reason for MM to lawyer up with white collar defense attorneys, imho, is the massive multiyear archive trading data about to be available to Plaintiffs from FINRA.
Market Data 
Markets 
