You're forgetting the "people who don't care, they just want to be seen looking like they care so they make a bunch of noise" factor.

Once you multiply the safety problem by the this factor it all makes sense.

A small non-problem that every screeching jerk will be exposed to is a bigger actual problem more likely to get addressed than a potential real problem that will mostly go unnoticed.

Also rear doors are kinda optional. They still make 2door 2-row cars. Heck, they made 2-door 2-row SUVs pretty recently. And child safety locks are a thing. So there is an argument to be made there (not that I think it holds up on modern stuff).