It's not just a resource limit issue. It's more akin to designing the tax code. At the top, you have to design a performance review system that trickles down to 100k people who operate in different parts of your organization without special casing too much to incentivize the desired behavior (special casing or discretion may add complexity, potential unfairness and bias, or effectively segment the company reducing internal mobility or make some products less attractive drawing away subsets of talent you may need there). To make the matters more difficult it's not like the CEO gets to write it on a tablet; as with the tax code, it is not designed in a vacuum, and the people who write it have existing political incentives too. Life is complicated.