When it comes to smartphones, most devices have a shelf life of around two years. That's from launch date to the time you usually stop seeing them being sold through whatever outlets you were able to purchase them. Whenever that shelf life ends, those devices get discontinued and they leave the official channels through which they're sold. It might come as a little bit of a surprise then that Sony has already seemingly discontinued the Sony Xperia Z3 Compact device which only officially went on sale in the U.S. towards the end of last year, which is really no more than about eight months ago.
For interested consumers who were wanting to get their hands on one of these devices through official U.S. channels, if you pop on over to the Sony Store US and proceed to search for and click on the Xperia Z3 Compact, it has disappeared from the main set of products. It now sits under the store's "discontinued products/discontinued mobile phones" category. The downside for this is that those who like to purchase devices from the official OEM website, no longer have that capability. There is of course the option of grabbing the Xperia Z3 Compact from other online avenues like Amazon or eBay, but there likely won't be a full spread of options in every color like through the official US Sony store, and chances are you'll be getting the factory unlocked international models.
Why Sony may have decided to discontinue a device which isn't that old, especially when they're still selling models of the original Sony Xperia Z1 Compact is strange. Since the device is listed in the discontinued section and not merely as an "out of stock" product, there is also no likely possibility that Sony has plans to reintroduce the phone at any point, but nothing is impossible. Whatever Sony's reasons are for pulling the device, You can still get a hold of it elsewhere, for now at least, and who's to say that Sony doesn't have plans to put something else out in its place, like a compact version of the Xperia Z3+ perhaps. You could also opt for a different model phone entirely, like the regular version of the Xperia Z3 which isn't that much bigger and won't cost that much more.