Imagine if you could only see in a very narrow portion of the visible light spectrum, like only green or something. That's kind of how radar "sees" (I'm grossly over-simplifying here but point is it doesn't see the way we do).

It's hard to tell something sticking off the back of a truck or a motorcycle behind a vehicle without false positive triggering off of other stuff and panic braking at dumb times, something early systems (generically, not any particular OEM) were known for, which is why they were mostly limited to warnings not actual braking.

And while one can make bad faith comments all day about that not technically being the fault of the system doing the braking allowing such systems to proliferate would be a big class action lawsuit, and maybe even a revision of how liability is handled, waiting to happen.