What reasonable company would justify spending tens of thousands an hour on server costs, when they could optimise their code a little more and run it for free?
So let's assume that the average person wanting to play SimCity is running a Core2Duo (released 7 years ago). It's hard to find benchmarks directly comparing a Core2 E6600 to something like an Ivy Bridge Xeon that you'd expect to find in a modern dual-socket 1U server, but even looking at a TomsHardware chart of x86 core performance can tell you that an i7-2600k is only about twice as powerful as a Pentium 4 HT660 (core-for-core) http://www.tomshardware.com/charts/x86-core-performance-comp...
Bottom line, the total cost of ownership doesn't at all make business sense to do right now. In 10 years, it very well might.
The core-for-core thing makes a huge difference in the real world that doesn't show up on single-core benchmarks. The HT660 was a good chip in its day, but it's at a four-to-one disadvantage for code that's multithreaded and/or running on a busy PC.
I think Sandy Bridge is my favorite CPU of all time. It does a truly massive amount of work without consuming significantly more power than the part it replaced.