Why unreal engine is not open source?

like godot has this feature that when there is a bug.
You can fix it by yourself. And if you miss a feature or you need a tool and its not there can i add it ?
I know i get access to the source code but can i change the source code only for myself ?
And that i need to pay 5% of the money i make. For me that dont matters.

So final question is : Can i add featurs to UE4 and pay 5% of the money i make dont matters
so can i do that ?

Tanks In Advance

You can download unreal engine’s source code on their github page. There, you can edit its source code.

You have asked this question at least 5 times in the last couple of days and received multiple valid answers to your question. What more are you looking for, or what is not clear?

Tanks In Advance

What LogierJan said. How many times do you need to ask the same thing? You can fork the engine, write plugins, submit pull request, expose C++ functionality to BPs…

Can i add featurs to UE4 and pay 5% of
the money i make dont matters so can i
do that ?

Yes, for the 6th time…

Tanks In Advance

am sorry