Ugh…
This is exactly why a proprietary graphics API for a niche operating system is a stupid idea.
Keep in mind that this is not Bethesda, but Zenimax Online. Most likely, not a single programmer who ever worked on a Bethesda Elder Scrolls game (let alone the upcoming iOS spinoff) has contributed a single line of code for ESO – or vice versa.
Even taking iOS into account, the Metal ecosystem is still dwarved by all the platforms that do not support it. Furthermore, I would bet that 99.9% of all developers who in theory could come into contact with Metal by supporting iOS or macOS don't actually have experience with that API, as they are either using ready-made engines like Unity or UE4, or use Apple's own abstraction layers like GameKit.
That makes Metal experienced developers a rare commodity. It probably wouldn't pay off for Zenimax Online to try to find and hire one these exotic beasts just to provide proper support for a tiny fraction of their userbase.