The thing is, even a 13 year old Core2Duo or Core2Quad machine will happily run Windows 10, Office, Chrome and browse the internet. Put an SSD in said machine and they'll be perfectly usable. Heck, add an old and cheap Nvidia 750Ti and you'll be able to play most modern games.
It's easier than ever to keep old machines chugging along, so there's even less reason for poeple to upgrade when Windows 10 upgrade was free and they use their phones/tablets for most other things.
I'm sure the PC Hardware market is buzzing along as well as ever!