Performance, I assume. Right now it may look like the wrong tradeoff, but every day in between incidents like this we're instead complaining that software is slow.

Of course it doesn't have to be either/or; you can have fast + secure, but it costs a lot more to design, develop, maintain and validate. What you can't have is a "why don't they just" simple and obvious solution that makes it cheap without making it either less secure, less performant, or both.

Given all the other mishaps in this story, it is very well possible that the software is insecure (we know that), slow and also still very expensive. There's a limit to how high you can push the triangle, but there's not bottom to how bad it can get.