What the UPBGE guys are working toward is essentially turning Blender itself into a more powerful version of the BGE (ie. Blender is the game engine, not a 3D app. with an engine attached). However, the GPL being the license means extra steps need to be taken to minimize the risk of someone changing out the assets in your game and selling it under a different name (which is why the majority who want to use FOSS, but have commercial ambitions use an engine like Godot instead).
Now I am not saying that commercial games have not been done with UPBGE (as there are a few titles on Steam actually), but you are required to provide unrestricted access to all of the .blend files used in the title (which the player can reverse engineer and modify freely).