- Most notably: the windows driver relies much more on the standard stack (its a DRI stack, it uses Xrandr for multi-display, etc.)
That requires some resource (mostly programmer's working hours) to adapt. And as (currently) Linux is a much smaller market, they can't pour that much (from their limited resources) into this specific task.
See this. Search for the string "million". Teslas are plain normal GPUs, like FireGL. AMD simply missed the chance here, which it can retake with opensource driver (due to lower maintenance cost and dependence on provider).