https://www2.law.ucla.edu/Volokh/rescue.htm
Duty to report are on the books, including in Massachusetts (ch 268 §40), requiring bystanders to report crimes, but not necessarily render aid. Duty to report laws are rarely enforced, which is what makes the Seinfeld setup more ironic. Although MA has one of the broadest duty to report laws (covering armed robbery and manslaughter in addition to sexual assault), the max penalty is a $2500 fine, but other states have jail time penalties. Duty to rescue is most always only for special relationships, such as parent/guardian/child, spouse, employer/employee, passenger, not random bystanders.
https://www.findlaw.com/legalblogs/law-and-life/in-which-sta...