Do you mix game development with engine? Of course an engine doesn't make an innovative game by itself. An engine is - hence the name - only the means to an end to help develop a game. Innovative games are all over the place in regards to the engines they use; from in-house/custom to products like unity, unreal, etc.

That you have the impression that engines like UE and Unity are "less innovative" by judging released games just shows how many games are developed using these engines - especially Unity. It's so damn easy to build games with it, that many people do, even when they only build something simple. And that's fine ... it means that more people can channel their creativity into game development, even when it doesn't yield anything ground breaking.

It also shows, though, that developers can focus more on the game development and have to deal less with engine development and now even asset creation, since these engines also bring asset catalogs. So it's really quite a good time to dive into game development, which fosters creativity and in the end there will also be innovative games among them.