The amount of churn in the computer industry is staggering and the upgrade treadmill is a huge waste of resources to many, but I suppose it's the only way for them to continue making a profit. Personally, I think Windows as an OS reached its pinnacle sometime around the XP timeframe; since then it has mostly been frustrating UI changes and feature removals, "security" features designed to lock down your PC against yo…
I am not familiar with the technical details of XP, so these are mostly observations from a user and not developer perspective:
1. On my old Pentium 4 box with 256 MB of RAM any release after XP hardly met the OS requirements. Yes, hardware has come a long way since then, but IMHO there is no technical reason why a kernel with a bare bones desktop needs more than this amount. I never understood why Microsoft's recommendations for RAM went up to 1 GB and beyond. My pretty standard Arch Linux setup in 2016 does not take more than this right after boot.
2. XP had a rather long lifespan as an OS. It was only later that Microsoft got into the 2-4 year upgrade cycle, hoping customers would purchase a lot of the upgrades. What happened actually in many cases was a simple skip of alternate upgrades, concretely Vista and 8.
XP definitely had some pretty bad problems, like the fact that it was not really ready for the 64-bit era, manifested in things like the 2 GB limit on memory per process. I don't know about what they did with the 64 bit XP version; it looked a lot like a stop gap solution.
I used the EOL announced for Windows XP support as a nice excuse to get myself to use a GNU/Linux system. I have not looked back since then.
As an aside, there are still some holdouts of XP usage, such as some lab equipment software written many years back. In fact, Windows XP embedded was supported all the way till January 2016.