Prebuilt PC sales is likely that cause. I'm sure AMD has a much higher share for those who are building their computers. But that is most likely an overall small share of the market of computers sold.
The Amazon statistics show much higher sales of AMD CPUs than of Intel CPUs, so this supports your belief about DIY computers.
Most computers sold are prebuilts, and most computers sold are for commercial use, ie office bees, so video game oriented PC's are a relatively small corner of the market.