Many didn't, presumably so they could continue to parlay their degrees for more money in the marketplace, with impunity (they could always claim ignorance, later). The FBI report stated that LaSalle had only one faculty member serving 15,000 students (and her only degree was a Bachelor's from LaSalle).
Many didn't take action, likely to continue profiting from their degrees and earning more money. They could easily claim ignorance later if caught. The FBI report stated that LaSalle had only one faculty member teaching 15,000 students, and her only degree was a Bachelor's from LaSalle.