You don't understand how the simulation hypothesis is related to "the branch of philosophy that deals with the first principles of things, including abstract concepts such as being, knowing, substance, cause, identity, time, and space."?

Tangentially sure it is, but it seems like a more concrete matter than what I would think of as a typical metaphysical topic.

Is it really more concrete than the traditional big metaphysical questions like: "why is there something rather than nothing" or "is there a real external universe outside of the mind"?

If anything, the simulation hypothesis seems to be an attempt to partially shed light on those traditional metaphysical questions. I would say the hypothesis is not tangential but directly bears on metaphysics.