Do you have a source for "no plans on adopting Vulkan"? Apple is definitely on the Vullkan working group (logo is part of the image at the bottom of https://www.khronos.org/vulkan).
It is a gut feeling from an old dog that has seen corporations change their stances in technology too many times.
Why adopt Vulkan given their investment in Metal, to the point that they have moved their accelerated 2D stack to Metal.
What is the point to rewrite it again for Vulkan?
Even if they adopt Vulkan, most likely would be a layer on top of Metal.
As for being in the group, Sony is also and they don't use OpenGL on their consoles.
Apple saved OpenGL from extinction when it was chosen as the iOS 3D API, as the API never had a foothold on game consoles.
Apparently now they are done with it and with no plans on adopting Vulkan.