I think the difference is those are, for the most part, internal safety features for the car's driver and passengers, whereas self driving effects mostly people not in that automobile. Sure, there are some features in cars that aren't, but for the most part, a driver knows (should know) their vehicle, and someone driving a 1978 station wagon and someone else driving a 2018 Volvo won't make that much of a difference on the roadways. Driving a car with a bad autonomous mode vs. a car with a good autonomous mode could be a significantly bigger difference for pedestrians and other drivers than older and newer cars.
That's quite apart from any safety features like air bags or ABS.
For instance, I could easily imagine that some cars might have more powerful kinematic-prediction software+processors and therefore are able to use smaller safety margins, allowing for more aggressive/liberal driving-behaviors than would be possible to safely perform in self-driving systems that aren't so well-endowed.
(Then again, depending on how good the first batch of general-purpose self-driving systems are, it may be possible that traffic safety margins among the self-drivers will be reducible enough that even the base models are "good enough" for anyone who doesn't encounter too many meatbag-drivers on their commute.)
Brakes, handling, visibility - better car - better response - safer for others. Also being lighter lowers potential damage impact. Not to mention stuff like sleep at the wheel detection etc.
As an aside, strangely the Great Recession apparently improved safety during, even when adjusting for miles traveled.
It's not something people realize because they think car safety improvements slowed/stopped once airbags became widespread. But really, the mid 2000s are when cars began to get very safe. By 2011, the NHSTA had to make their star rating system much more strict because nearly every car had a achieved a five star rating.
A Volvo 940 from about 1993 head on at 80mph with a 2004 Renault Modus - the first small car to get 5 stars in the new Euro tests.
I would have bet on the Volvo. No. Dramatically no.
I’m also not sure why everyone hasn’t adopted the Toyota model of including basic safety tech in all trims...
Sure, but that's what actually happens over time. First airbags are introduced, then we get some evidence that they actually work, more manufacturers introduce them and we get even more evidence, then eventually the law requires them.
It's necessary to be deliberative before mandating things because not everything is a good idea, e.g. automatic seatbelts in the 90s.
They already do this with everything else. Vehicles like Mercedes and Tesla are significantly safer than some competitors. Legislation sets the floor, not the ceiling. Or at least it shouldn't create a ceiling.
And it's also the case that SUVs and other large vehicles pose a greater risk to pedestrians and other motorists than smaller ones, but legislators haven't done anything about that.