Because that's not an official Microsoft list and is maintained by who knows who. There are two official compatibility ratings, "Certified for Windows Vista"(https://winqual.microsoft.com/member/softwarelogo/certifiedlist.aspx) and "Works with Windows Vista" (https://winqual.microsoft.com/member/softwarelogo/workswithlist.aspx). VFP 9.0 is on the latter list.

>I wonder what it means that that Visual Foxpro isn't on any of the lists - "Works", "Minor Problems", "Heavy Problems/Incompatible".