One reason for this is because a game engine is so huge and complex that they have a massive learning curve, much more so than any web framework. If you use Un

One reason for this is because a game engine is so huge and complex that they have a massive learning curve, much more so than any web framework. If you use Unreal Engine / Unity, you have a pretty big pool of talent that is already proficient with the engine and can hit the ground running, rather than having weeks of learning the intricacies of your specific game engine.