The curse if it exists could have come from anywhere. It didn't have to start with Buddy Holly. Ritchie Valens avoided a previous plane crash in his schoolyard in Pacoima when he went to his father's funeral. Music producer Joe Meeks dabbled in the occult and warned Holly about the date February 3rd and later killed himself. But I think it's a general rock-and-roll curse if you want to call it that in combination with other factors that might not exist to the same extent today with things like new regulations in flying and medical care and rehab.
I don't think today's regulations would have prevented the crash because such things still happen. JFK Jr. shouldn't have been flying at night, but that didn't stop him. Small planes are constantly crashing and most of the time, it's due to pilot error.