How come it's not the same for Windows? Sure, there are a few enthusiasts around the world who will go the extra mile to get their hands on the beta version, but it's far from a general worldwide phenomenon.
Basically, some won't want to upgrade. Most will wait to buy a new PC. Others will download an illegal copy, taking the risk of exposing their personal stuff to the "World Wild Web"...
As those Windows users are probably also iOS and Android users, they should crave for the next Windows... And this is not the case.
Assuming that Windows users were able to adapt to the new environments proposed by iOS and Android, could they consider the fact that an alternative to Windows would be as useful and fun on their PC? Have they heard about Ubuntu (and friends)?
They will hack and crack MS Office to get it free, they will install many tools to get Windows more useful, they will fight against viruses and adwares and spywares with the latest anti-virus available. Managing a Windows PC does require a lot of personal time.
With iOS or Android, you simply do nothing. Load it up, upgrade all your apps from the store. Get free OS upgrades when available and enjoy your device without thinking about it. What if I would tell you that you can get the same experience with Ubuntu?
Don't believe me? Try it out for yourself as you can download Ubuntu for free (ubuntu.com)
Nothing illegal here. It's free simply because it is open source stuff.
Don't like Ubuntu? Try out one of its derivatives like Mint or Kubuntu. The choice is yours.
Maybe it's time to start using your computer instead of managing it. Get Ubuntu!