In addition to testing in advance that your own (hard|firm|soft)ware will work, some people will just want to get new features early and are willing to deal with the potential extra bugginess.
At the time, XP was 6-7 years old, and the screenshots of a shiny new Windows OS made me so itchy to try it out. Vista looked magical compared to XP just before release, it was the dawn of the frutiger aero aesthetic too. Very optimistic vibes back then.
Ha, I remember dual booting Ubuntu and wrecking the bootloader, rendering my machine unbootable. Fun times, lol. Taught me a lot, though.