That's not how it works, first of all IdTech is not a general engine, it's only made to build specific games: fps.
Next you need to make a product out of that meaning a very large investment so that the engine is actually usable outside of ID, people that don't know what an engine is think of the rendering part but it's actually very minor compare to pipelines ect ... which we know nothing about, it might not even be good or painful to use.
Unreal is widely used because it can create any kind of game and the pipeline, tooling are good and well integrated.
A lot of unreal engine games also fork the engine. If your bar is being forked then unreal doesn’t meet the bar for a lot of people either.
3D Engines of that fidelity are rarely genre specific. Editors might be but the engines are often fairly flexible because most genres share a lot in 3D space.
Next you need to make a product out of that meaning a very large investment so that the engine is actually usable outside of ID, people that don't know what an engine is think of the rendering part but it's actually very minor compare to pipelines ect ... which we know nothing about, it might not even be good or painful to use.
Unreal is widely used because it can create any kind of game and the pipeline, tooling are good and well integrated.