Laws about fireworks are fairly recent, and they vary wildly from state to state. Where I grew up private fireworks were illegal, but every town and city had official fireworks displays that were really great. A few people would drive out of state to buy things, but that was exceptional.
Remember that all these laws about seatbelts, etc. were only passed against stiff resistance. There is a streak of “Don’t tell me what to do!” in the American psychology, so it’s not so legal to get the law passed, and then to get people to obey it.