Thicke 'nem may have offered that $ to make the Gaye family go away. they may have thought it was cheaper to pay them those six figures (to be paid by all the defendants, not just Thicke) than to defend a suit filed by the Gaye family. had the Gayes filed suit, the defendants (Thicke 'nem) would've had to pay for attorneys and those fees ("WHY DO I HAVE TO PAY ATTORNEY FEES??!?") may have ended up costing the defendants more than whatever they offered the Gayes. if the Gayes had accepted the $ they would've probably had to agree not to file a suit, and the defendants likely wouldn't have had to admit wrongdoing. so the defendants would've saved money going that route.

this is common stuff in civil litigation. it happens everyday.