Because if it did, then that means that without the plane of voltari, Etheria would be entirely unmagical. That means that underneath all the magic they must have some sort of normal physics that everything operates on. This makes it difficult to explain the existence of all of the gods and all of their many portfolios, as well as the other planes of existence overlapping Etheria. Because if Etheria ran on normal physics or some variant of it, then that means that most or all of the natural phenomenon and human activity that happens should be able to arise naturally, whether or not there were gods or other planes of existence. And they're not even all human per say. Amongst the sapient beings we've been introduced to so far are elves and orcs and dragons and demons. How would a wizard explain their existence? Just that "the realm of voltari did it" or "someone cast a spell to make them like that"?
So now I'm wondering: does all magic really come from the plane of voltari? Based on the existence and powers of the gods, and the existence of the other planes of existence, including the elemental planes (which seem to work on Aristotellian physics what with the four classical elements and all, which might make sense for magic but not at all for a nonmagical physical system), it seems more likely that magic is innately a part of their world.
I'm rather curious about this, and I need to know for a story I'm trying to write.
Thanks!
(Also, if there is readily available hard-evidence that Etheria has gods, and a large number of the Wizards of Sortilege, who are supposed to be rationally-minded magical researchers, STILL turn out to be atheists, I will be calling bs on those Straw Vulcans.)