Because even braking can't avoid the crash. Unavoidable crash means bad juju if the 'self driving' car image is meant to stick around.

Breaks require a sufficient stopping distance given the current speed, driving surface conditions, tire condition, and the amount of momentum at play. This is why trains can't stop quickly despite having breaks (and very good ones at that, with air breaks on every wheel) as there's so much momentum at play.

If autopilot is being criticized for disengaging immediately before the crash, it's pretty safe to assume its too late to stop the vehicle and avoid the collision

So, as others have said, it takes time to brake. But also, generally speaking autonomous cars are programmed to dump control back to the human if there's a situation it can't see an 'appropriate' response to.

what's happening here is the 'oh shit, there's no action that can stop the crash', because braking takes time (hell, even coming to that decision takes time, activating the whoseitwhatsits that activate the brakes takes time.) the normal thought is, if there's something it can't figure out on it's own, it's best to let the human take over. It's supposed to make that decision well before, though.

However, as for why tesla is doing that when there's not enough time to actually take control?

It's because liability is a bitch. Given how many teslas are on the road, even a single ruling of "yup it was tesla's fault" is going to start creating precedent, and that gets very expensive, very fast. especially for something that can't really be fixed.

for some technical perspective, I pulled up the frame rates on the camera system (I'm not seeing frame rate on the cabin camera specifically, but it seems to either be 36 in older models or 24 in newer.)

14 frames @ 24 fps is about 0.6 seconds@36 fps, it's about 0.4 seconds. For comparison, average human reaction to just see a change and click a mouse is about .3 seconds. If you add in needing to assess situation.... that's going to be significantly more time.

AEB braking was originally designed to not prevent a crash, but to slow the car when a unavoidable crash was detected.

It's since gotten better and can also prevent crashes now, but slowing the speed of the crash was the original important piece. It's a lot easier to predict an unavoidable crash, than to detect a potential crash and stop in time.

Insurance companies offer a discount for having any type of AEB as even just slowing will reduce damages and their cost out of pocket.

Not all AEB systems are created equal though.

Maybe disengaging AP if an unavoidable crash is detected triggers the AEB system? Like maybe for AEB to take over which should always be running, AP has to be off?