The editor can be shipped by game developers. That being said, if the developers wish to ship editor or their own custom engine, they are bound by EULA section 4.a.i. (the editor falls under the definition of “Engine Tools”) which states:
Any public Distribution of Engine Tools (e.g., intended generally for third parties who are separately licensed by us to use the Engine Code) must take place through a marketplace operated by Epic such as the Unreal Engine Marketplace (e.g., for Distributing a Product’s modding tool or editor to end users) or through a fork of Epic’s GitHub UnrealEngine Network (e.g., for Distributing Source Code).
It is common for game developers to therefore split up their modkit files into a number of chunks under 2GBs and place them under the releases page of their fork of the UnrealEngine repository. Therefore, users must have an Epic Games account to download these files.
There are also some special cases where developers have gotten a special license to distribute their modkit files through other platforms, for example through a Steam download (ARK, Satisfactory).