I've looked all over the Internet for <16" short-depth cases multiple times over the years, and I've learned the most important question is this: what do you want to put in it?
I'll tell you right now that some of the things I've wanted, like...
-
A 2U with hot-swap caddies all the way across the front (like this or this, but <16" deep at the cost of fitting only an ITX motherboard), or
-
A 4- or 5U chassis that can fit an EATX / SSI EEB (12"x13") motherboard and an ATX PSU at the same time, or
-
A chassis of any size that has both the motherboard/PCI I/O and the drive bays on the front (front drive bays are normal and you can get front access I/O, but not both at the same time)
...simply do not exist, as far as I can tell. I'm pretty sure all of these things are geometrically possible (I did the math), but apparently I'm the only one who wants such weird stuff.
You can get a basic-bitch whatever-U case that supports a mATX motherboard and hard-mounting a couple of internal drives, with sharp metal edges, a shitty plastic door, and a price double (or more) what similarly low quality would cost in a desktop form-factor all day long, though.