> In this case, I have a feeling that is a pro not a con. Because this file is so core to the system, and has so much complexity, that breaking it up into smaller parts could cause a dev to feel like they understand it only to find out they don't after it's released.

I think you're on the money here. This was done intentionally, to ensure that devs understand the whole thing before making changes, because the functionality is so critical and so easy to mess up.

Also, breaking single logical things up into smaller files (rather than into a composition of smaller logical things) just leads to unneccessary file hopping and wrecks locality of reference for the dev.