That chart is the PREDICTED hashrate distribution IF everyone would use stratumv2. They show that chart as a reference to how much INDEPENDEND miners there probably could be, IF the block template process was not centralized.
I know, but it's still true in a sense that there's countless of individual entities mining around the globe. Mining operations are not centralized at all! I'm not saying that everything's perfect and I believe we should focus on to talk about mining pool centralization or ASIC manufacturer centralization, but those are very different topics.