Some software used to check that the version name string started with "Windows 9" to determine if it was running on a "Windows 98" or "Windows 95" system as opposed to 3.x, NT, XP, etc. Yes, there are internal major and minor version numbers available, however that didn't stop people. Ergo, jumping straight to "Windows 10" which would cause software that did this to find "Windows 1" in the string triggering a message like "This program requires at least Windows 95..." or whatever instead of immediately crashing because it made a system call to an API that hasn't existed for 10 years. Or worse, silently corrupting data because of other OS API changes.