Microsoft chose to stop developing Visual FoxPro to concentrate their resources on other products in their line. During this window, they will provide bug fixes, provide upgrades and otherwise generally support their product.
Microsoft commits to supporting a particular version for a certain period of time. They cannot support every version of their software indefinitely. For commercial organisations like Microsoft, they are continually releasing new software to take advantage of the improvements in new hardware to make our lives easier. When any software is developed it has an expected lifetime.
