Because there’s no demand for it. Currently production is very dirty but the engine itself is green as it gets. As the demand shoots up government can and probably will stimulate green production of hyrdogen. Point is, once you have hydrogen car there’s no upgrade path needed anymore. Initial ICE engines were of poor efficiency but it got better. But we have to pick technology which can scale with demand. Batteries are simply not it, especially when it comes to big transporters like boats and trains. You can’t use batteries on those. Even trucks are problematic as battery weight significantly reduces amount of cargo.