Apple not supporting Vulkan is a business decision. They wanted a lean and easy to learn API that they can quickly iterate upon, and they want you to optimize for their hardware. Vulkan does not cater to either of these goals.

Interestingly, Apple was on the list of the initial Vulkan backers — but they pulled out at some point before the first version was released. I suppose they saw the API moving in the direction they were not interested in. So far, their strategy has been a mixed bag. They failed to attract substantial developer interest, at the same time they delivered what I consider to be the best general-purpose GPU API around.

Regarding programmable tessellation, Apple's approach is mesh shaders. As far as I am aware, they are the only platform that offers standard mesh shader functionality across all devices.