It is more expensive to keep a game engine kind of generic while developping a game. Usually the game engine will end-up being taylored for a specific type of g

It is more expensive to keep a game engine kind of generic while developping a game. Usually the game engine will end-up being taylored for a specific type of game. Namely, diverting for that type of game won't feel right or even will work badly. It may explained why games based on the same engines feel all the same (just a skin swap, zero flavor): game devs don't want to divert from what the "usual" and optimized usages of a game engine, because they don't want to have to deal with engine internals (or they cannot due to closed source) for the very good reason which is: most of the time those engines are insanely complex and massive (and that includes their SDK too). All that to said, there is no magic bullet. Maybe some functional and completely siloed modules may give more flexibility to game devs, but they will work out the glue.