Because they unsolved the problem for some reason. Probably cut a deal with major locksmiths.

You locking your keys in your car a dozen times doesn't equate to proof of manufacturers programming cars to intentionally lock keys inside of them.

These systems are typically time-based around entry/exit not the location of the keys. You're telling me every one of these dozen cars would automatically lock the vehicle if the keys were left inside but never lock if you took the keys with you? That's supposed to be "more secure" than just locking the car 3-5 minutes after you get out and shut the door? With many vehicles being keyless now allowing you to unlock the door by just grabbing the door handle with they key fob in close proximity, how would that even work?

Furthermore, the only security present with keys 30 years ago was a tiny RFID embedded in the key that could only be "read" by the vehicle when it was in the ignition barrel, so how were these vehicles determining that your keys were still in the car? Always-on proximity sensors for key fobs only became a thing with push-button start in the 2010s.

Your old school key fobs were nothing more than 'dumb' garage door openers or TV remotes that only transmit when a button is pressed and only receive if the transmission is close enough to the receiving antenna, meaning neither one knows the position of the other. My TV remote will work the same whether I'm using it in my living room or standing in my front yard pointing it through my living room window. Neither the TV nor remote 'know' whether I'm standing inside or outside my house while pressing a button and they certainly don't know where either is located when I'm not pressing button, so how were cars doing this way back in 1996?

You heard me

Three decades