Have you actually taken a look at it (the source code?). It's actually very well written and easy to understand even for me (a sysadmin, not a programmer). I have a side-project in ue4 that I've been trying to dev on gnu+linux only and have been working hard to avoid the issues that games like pubg have that make them unable to run on linux (mostly because Epic has not been taking care of us linux users like they promised and the marketplace assets often only work on windows, so when a dev like the pubg guys just throws a bunch of assets in, that's why they can't get things to work on linux)

My problem is I don't know much C#, but it really confuses me why Epic decided to use C# for the framework of a C++ engine...

That project is on hold while I play with vulkan directly via https://github.com/KhronosGroup/Vulkan-Hpp.

I have too many projects.