You're taking the problem in the wrong order, it's more why would I use Godot which is vastly inferior to unreal and unity.

Now what is inferior, well performance is bad, they have their own scripting language which no serious dev would want to use, they have c# integration but it's not on part. Assets, tooling is also inferior, you can't make console game with Godot etc...

Networking wise Godot has not much either.

That's the difference between an open source engine with not much investment and 100's $ put into unreal and unity.