Then, almost 8 years after WinXP's launch, MS released Win7. There's a lot of improvements between the 2, but I wonder what were the major factors that made users upgrade to Win7. I only remember a few pain points in XP that were relieved in Win7: file/app search, connecting to the internet, system updates, and window management.
64-bit memory space support (crucial, considering enormous browser bloat after the FF 3.5 era)
TRIM support for SSDs (I switched to 7 when consumer SSDs started to become affordable)
DX11+ for gaming (DX10 was a wash in Vista, but by the time I switched to 7, there were some games that actually did look noticeably better with DX11)
Half-Open connection fix for torrenting.
But I'm a power user, so reasons for regular users may vary.
There's also the factor of familiarity to consider. People buying new machines will learn the new system, and overtime as they learn how to use it, they will prefer it to older system versions. However, this is another long-term factor, and as such Windows 10 seems doomed to only slowly gain adoption.
Note:
Considering the reputation Windows 10 got for itself at launch, this is less surprising. For non-technical users, the upgrade to Win10 has probably been pointless or frustrating: new concepts, new default applications and system UIs these users have learn to perform their ordinary tasks. What's more, for many users, upgrading their system to Win10 left them with an unusable machine. Win10's launch was a mess.