If you're working on a small game project without an existing framework/platform, you usually build a really bargain-basement game editor alongside it. That editor takes a long time, and it's often spent in arranging UI stuff.
If you're already using Blender to make assets, there's some benefit to stuffing Blender's UI into your game editor too.
If you're already using Blender to make assets, there's some benefit to stuffing Blender's UI into your game editor too.