If you had beefy enough hardware, which we all eventually did years after XP came out, it ran as fast and almost as stable as 2000.
If you didn't mind the bland theme, and wanted higher FPS while gaming, with more responsiveness (less of a delay when double clicking on a window, for example) then running Windows 2000 over XP was a no brainer. In competitive first person shooter circles at the time, people preferred Win2k to XP for these reasons.
I have a soft spot for Windows 2000 because I was very impressed with it when it first came out (coming from Win9x), but there wasn't much point to using it over XP after XP came out. Windows XP is just an improved version of 2000, and it was updated for much longer. Windows 2000 doesn't even support wi-fi without third-party utilities.