Why this is important:
Given what we see in the cosmic microwave background, the first light we can detect after the inflation of the universe, structures can only grow so large within our current models. Yet this, and other similar discoveries, appear to be larger than our current models predict.
I read a really excellent breakdown of this years ago that I'll attempt to paraphrase:
Modern-day guns are the endpoint of centuries of evolution! Evolution that, at nearly every step, is trumped by either magic or a simple bow and arrow.
Which isn't to say that guns can't or wouldn't exist in a fantasy world; "metal tube with an explosive that shoots something out" is fairly intuitive design.
But that basically gets us to, what, blunderbusses? Or maybe something even less functional, I'm no historian. Point being that, in a world with magic, innovating on a boomstick that has an effective range of ten meters may not be an attractive use of time when you have other, better options.