Why is Windows XP professional (installation disc and license) still selling on ebay?

There are many old computers. For OS like Windows 8.1, it requires more higher specs. XP still has use to run older programs

Millions of people still use it and on older systems that can't take the upgrade it's sometimes not a matter of choice. I know a fellow still using Windows 2000.

I have hundreds of peolple still using it. It is mostly very safe but MIGHT be vulnerable if anyone bothers to wate the time trying to find a security hole and creating an XP exploit.

Some people still us XP. It still works but it is not being updated and new printers and such may not have drivers produced for XP.