>it's either useful and I'm better off remembering it, or it's useless and I don't even need to write that down
No, that's obviously not how the universe and information work. Pareto principle here at play as well.
> Why aren't our brains better places for this
Because they aren't. That's a strange question. Reality is reality.,
Our brains are not made for remembering (rote memorization; a mere 3-7 items can be short-term remembered and juggled with at one time), but for thinking and making connections.
Computers are amazing at storing information, but can't think.
If one is smart, he utilizes the strengths of tools/opportunities that are available to him instead of using them inefficiently.