Super curious and I've been meaning to ask forever, as I've never really seen such a unique combination before. What's the mentality behind power on and waiting until the credits?

Thanks in advance for any answers. :)

I am not 100% sure about the answer to this question so I apologize if I give you wrong information... but since no one has answered you yet I am responding to give you an idea of why (to the best of my abilities/understanding) and its because we time it through game timing, not RTA (meaning the start of the game Power On all the way to the end being the credits) rather than timing it from first input/last input. Anyways hopefully this helps ~

I thought it was based on Japanese rules

The game was primarily run by Japanese runners early on. They used "JRTA timing", which times from power on to the credits. We have upheld the tradition.

Cool, thanks guys.

Neat to know that about JRTA as well. :) I had no clue.