I’m thinking this sort of thing didn’t happen when I was younger, in the days before cars were air-conditioned. In those days, crime wasn’t as rampant as it is today, and cars would become so hot after sitting in the sun, you didn’t have air conditioning to cool them off, so you left the windows open. Also, fewer people had cars and took public transportation more often.
Child restraining devices are the ‘cause’.
Nobody forgets a kid beside the driver in a booster seat with a little plastic steering wheel.