As someone who is periodically involved with this sort of thing, the challenge is that far and away the easiest things to objectively measure are almost always output metrics: commits, blog posts, external presentations at conferences, etc.

Output metrics chosen correctly also tend to represent things that the team/person has a reasonable degree of control over. For example, a developer KPI probably shouldn't be number of new customers because that's something they have vanishingly little control over, especially at an individual level.

The problem is that those things that a number of different teams are contributing to are probably the thing that the company cares about.