Because it's 90% psychological state, not prep or tactics knowledge. What constitutes elite pker is his ability to be relentless and operational ~100% of the time. Because let's be true - we lose PKs not because we lack knowledge or skill, we lose PKs because we: 1) drop our guard; 2) don't care enough; 3) go balls to the wall; 4) enrage and lash out etc.
Top PKer does not let himself do that shit. He's always intense and charged for PKs. That's what makes him elite. Applying this criterion, there're very few elite pkers in the latest history that I know of, and they are: shapa, beront, alex. Until recently - Twist and Marcus. And not currently active - Nep.