In my case, I want a stable OS. Also there's a high chance the Windows 10 video driver for my 4 year old Dell laptop is broken, just like the last 3 versions Dell released for Win7. Only the first one from 2012 has no bugs.
What makes Windows 10 unstable in your view? I'm no Windows fan, but I've been using it on my work laptop for a few months and have had no issues. I'm actually surprised by how much I'm not hating it.
If history serves right, I upgraded to Windows 7 around 2-3 years after it was released, and I still had occasional blue screens or hiccups. About one year later it finally started calming down. Now, in 2016, I could run my machine indefinitely without ever restarting (if not for updates). It's that stable. Going to wait at least 1-2 years before upgrading. I don't trust big companies anymore.
I think the OS itself is stable, but once you throw in a bunch of rushed drivers, a bunch of software that was 'fixed' to run on the newest windows and another bunch of outdated software, then something is bound to break.