Why should you care what other people do with their computers? When Microsoft rolls DRM into the OS, and marries the Windows to the BIOS, and congress decrees that all non-DRM-compliant computers are illegal "circumvention devices," then you will care very much that Linux failed to create a popular, open platform to prevent this from happening, even though the Linux development community was INCHES away from making it possible.
I have no problem with closed source software, but platforms and standards should remain open. Open standards are what made the Internet possible. They are what made the PC boom possible. And, if you care about open platforms and standards, then you should care about how many people use Linux.