Unreal Engine 4 on DirectX 12 works better than on DirectX 11

The user of YouTube CryZENx posted on his channel a video that represents the advantage of using the DirectX 12 graphics API on Unreal Engine 4. For comparison, he cited the same scenes from the Zelda fan project: Ocarina Of Time, demonstrating the frequency on the DX11 and DX 12.

This news should not be a big surprise, but since not many games on Unreal Engine 4 take advantage of DirectX 12, the effect is not particularly evident in titles. To date, the new version of the API is only used in Gears of War 4 and Caffeine.

Why do not developers introduce DirectX 12 support? Perhaps the extra cost of what they consider an insignificant increase in productivity.