system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 If in most cases "death" directly implies the lack of oxygen supply to the brain then why can't we develop a technology that directly provides oxygen to the brain in worst-case scenarios to prevent any shortage at all?

I'll make my question a little more clear. As far as I read, whenever a person is about to die, all that's happening is that their heart stops beating which in turn stops the brain's access to oxygen.

I read that it is possible to revive a dead person within 3 minutes of heart-beat-stopping as the brain usually has a 3 minute backup oxygen supply.

Why have there not been any research or investments in developing a technology like the "defibrillator" which revives the heart, but instead to keep the brain alive?

Also, question part 2: why does the brain die in 3 minutes? Why can't it be revived?
gpt
There are technologies that provide oxygen to your brain/body after your heart has stopped. 

How do you think they keep people alive during heart transplants that take hours?

The problem is that these machines aren’t small or portable. And to use them you have to tap into the blood vessels that travel to and from the brain. In order to artificially pump oxygen through the brain.

So, even if you were able to take the large machines in hospitals that replace hearts, and make it small and portable. You would still have to have emergency responders cutting open the patients neck in order to insert the tubes in the necessary vessels leading to the brain.  This would be a very dangerous and complex thing to do, even in an emergency room.

This is why chest compressions, which pump the heart by hand, are recommended for any amateurs/normal people trying to help someone with a stopped heart. It’s an easy and minimally invasive way to keep blood flowing to the brain.