Why does blizzard not bother with movement-speed anymore?

Tracer and Genji are still the only two heroes with increased base movement speed (+8.7% faster).

Why are they not using this for some other heroes? They never touch movement speed when it comes to balancing. They could use this to buff / nerf heroes in other ways than just changing damage and CD numbers.

^{Personally, I wouldn't mind if venture got the increased movement speed... but who am I to judge balancing.}