Because it cannot be mathematically developed. KPIs as class of algorithm are linear dimensional reductions from a complex hyperspace to a small, arbitrary reference system built on non orthogonal axes, aimed to capture non periodic, non stationary phenomena (i.e. that unpredictably evolve over time).
Mathematically, performance kpi do not make much sense for most jobs, unless the job is so straightforward that the hyperspace has such low complexity that KPIs are meaningful representation. Not even a call center job has such mathematical characteristics…
As a task, AGI is mathematically much simpler task.
However performance kpis are the only thing many have to judge, as they lack technical and personal skills to do otherwise. It’s a tradeoff, but we must recognize that kpi are oversimplifications with extreme loss of information, many time useless