National Highway Traffic Safety Administration passed regulations in the late 70's requiring active safety features of either an airbag system or automatic seat belts by the late 80's (the legal saga of those regulations coming into effect is its own long story). Then, in 1995, airbags became mandatory, so the automatic seatbelt systems became redundant for regulatory compliance. And culturally, by 1995 people actually were choosing to wear their seatbelts, so that the automatic seatbelt systems didn't actually make as big of a difference in practice.