Why are there so many Windows Server 2003 stragglers?

The strange afterlife of an unsupported operating system

Windows Server 2003 is almost out of support, and many of us simply don't have the option to upgrade to a newer operating system. In some cases this problem is self-imposed. In others it is the result of events beyond our control. Either way, there are millions of businesses - mostly small businesses - who simply don't have the option to upgrade even if they wanted to."