This NetworkSynchronizer module requires to recompile godot. Can a C++ developer explain why?

I am planning to use this module in my game, since it supports prediction and rollback/rewinding, unlike other similar modules.

Netfox supports those, but netfox is written in gdscript, which isn’t optimal for this sort of task.

Is there any C++ developer who understands how this module works, and why it needs recompiling godot?

I would rather not have to recompile godot.

Because they choose to make it a module. More info about modules:

The link says

C++ modules are mainly needed when GDExtension doesn’t suffice and deeper engine integration is required.

What exactly does that mean? Any example? And can you see how this module I linked cannot be made into a gdextension?