Why does WMP setup ask to reboot after the install?
Certain files can be in use by the shell which thus require WMP to reboot. If you wish to avoid this reboot, log out and back in previous to installing. WMP9 and newer should not require a reboot in other conditions, provided that WMP is not running at the point of install. WMP is pretty good about avoiding reboots if possible. If you’re asked to reboot, please do so before using the player – otherwise the player should block you.
Because it installs device drivers. Alternatives would have been to alert the user that that new device driver isn’t usable until after restart (which is the approach taken in WMP for XP and newer setups) or to shut down and restart the device – which isn’t necessarily possible/clean. Which installing WM Player 9 Series on Windows XP, certain files can be in use by the shell which thus require WMP to reboot. If you wish to avoid this reboot, log out and back in previous to installing. WMP9 and newer should not require a reboot in other conditions, provided that WMP is not running at the point of install.