CentOS 7, released with Linux 3, only went out of support a month ago.
Expect to see it pop up everywhere the coming five to six years. The sort of people who still run CentOS generally aren’t the sort of people who upgrade their software unless they absolutely have to. It’s like those ATMs running that obscure version of Windows XP and 7 (although the Windows 7 Embedded release will still receives updates for a few more months)), you deploy an OS onto them, kill any accessible port you can find, and just let it do it’s thing for a couple of years.
The only reason the DOS POS systems are being phased out is that the hardware they run on can no longer be replaced easily, and even then Dosbox is sometimes used to run POS software.