Price tag and pop culture. You see glocks mentioned in movies and rap songs all the time.
Like the Glock 7? It's a porcelain gun made in Germany that doesn't show up on airport x-ray machines. Bet you didn't know that!
I suspect you're joking... But for those not in on the joke: the Glock 7 existed only in a
Die Hard movie, not in the real world. It wasn't made in Germany... it was made in Hollywood!!
Even if the frame had ceramic components, the barrel and slide would still have to be metal (to withstand the pressures generated by firing rounds), and I've never seen a ceramic recoil spring or magazine spring. That would mean you've got a one-shot gun of unknown accuracy (one-shot because without springs it couldn't cycle, and the barrel, if it was ceramic, might self-destruct before the bullet exited)!
And then there's the problem of AMMO. It was only this past year or two -- long after the
Die Hard series of movies died their own death -- that a couple of firms came up with non-magnetic bullets. I don't know if there are non-metallic cases possible, but even if there are, I haven't seen any ammo with both case and bullet made of non-metallic materials.
Given all of that, I suspect a ceramic guns would be a world-class KABOOM the first time it was fired!!
And it's important to understand that just because something is non-metallic doesn't mean it will NOT show up on X-rays. (Hint: bones and other dense materials show up, too.)
A Glock 7, if it actually existed, would still show up in X-rays.