I'm new to speed running so I'm not fully clued in on reason for why things are chosen. When timing runs why is it based off of real time instead of the timer that's in the credits?

Game time and real time run differently. For a very basic example, game time will usually pause during certain points and works slightly differently. Real time never stops ticking once you start the timer until it is stopped by the autosplit or you end the run. That's my understanding of it.

It's so people don't spam the esc macro for the best movement and cursor placement most likely. If the menu didn't stop the in game timer then I'm sure they would probably use in game time. (I could be wrong for the reasoning though)