I've read about them and it's fascinating how it happens. Brain eating amoeba are super common, but it's actually rare that they kill you because they don't actually want to be in your brain, they just get lost and confused. There's a thread that connects your nose to your brain looks like food to them so they follow it up there. And your body just has a hard time killing it for some reason. Then it reaches the brain where defenses are weak and just goes wild eating, at which point you are done for.
I think of them like little lost sharks. They don't know what's going on or where they are, but they will mess everything up just because that's what they do.