This is irrelevant. With all major engines gaining Vulkan support this list will baloon fast.

A good gaming engine supports multiple graphics APIs, making specific ones irrelevant.

My point was, adoption in engines is relatively slow, but once it happens, things become easier. So current usage lists aren't a reflection of general progress. Unity for example gained Vulkan support in the latest version which came out recently, and Unreal is still not there (but already close). Same goes for Lumberyard.

Of course the tax on development imposed by lock-in freaks translates into that slowness. I.e. as you said, need for engines to support many balkanized APIs means slower releases to the market.