Caffeine is not a PED unless you're the sort to show up at the starting line sleepy. Maybe you don't care and have no adrenaline or fear to hype you up.
So they do tests on random sample and 20% of them are sleepy so they find some slight overall effect. Big deal. You could get the same effect by someone grabbing their shoulders and shaking them and screaming "wake up!"
So this is not a real drug, just a substitute for motivating yourself into an energetic mood. Can't make you do anything you couldn't do naturally.
Amphetamines CAN... basically long-term adrenaline that never lets up, removing physiological barriers to overexertion.