Adrienne Hall, Microsoft’s General Manager for Trustworthy Computing, explains Microsoft released the patch for Windows XP due to the proximity to the end of support for Windows XP.
Even though Windows XP is no longer supported by Microsoft and is past the time we normally provide security updates, we’ve decided to provide an update for all versions of Windows XP (including embedded), today. We made this exception based on the proximity to the end of support for Windows XP.Source: DailyTech