My parents use their computer to browse the internet, connect with people via social media and play browser based games. All these things are achieved with an average smartphone / tablet.
I use a computer to make software, do business, make artwork, play video games. A phone is nice but it will be along time before I'm running Visual Studio off it, a PC fits my needs.
I'll take a wild ass guess that most people don't need a desktop computer to do what they need, and that's why there is a shift, and why there is no need to realign them.
There is a market for desktop computing, it's just not nearly as big anymore.