Why don't people understand how 'personal testimony' can be used as evidence, and what it can provide supporting evidence for?

Very well. Here is my personal testimony.

I was hatched, thirty years ago, at a raven sanctuary. Being an inquisitive little bird, I learned to fly quite rapidly, then how to escape from my cage. But little did I know that the sanctuary was only a quarter of a mile from the now decommissioned Trojan Nuclear Power Plant. I didn't even know what a power plant was.

What I did know was that there was a large building with a lot of people, and I remembered I liked people. So I investigated. And I managed to sneak in to the power plant, unnoticed. Somehow, I got into the pressurized water reactor, and got a dose of radiation.

And that is how I became what I am today, a sapient raven capable of typing and speech, with a penchant for top hats.

Do you believe my personal testimony?

-Corvus Blackthorne

Personal testimony is not actually "evidence" but interpretations of that which some feel is special or divine in nature because they don't understand it. You seem not to understand the biblical presentation of a faith for it does not require "evidence" for one who truly has the "faith"! Almost all Atheists understand what a faith is and what a belief actually is.