Why are defenders more reliable on penalty kicks?

While I can't comment about football specifically, I can comment about very high level play in the sport I coach. If I had to speculate, it would be that a good team and goalie will review film of attackers at work and will know how they approach and look while shooting at different corners and where they like and don't like to shoot. Even in the event that a goalie has not done pre-game prep, by the end of the game they have likely seen several shots from each attacker and will be in a better head space to act against them. On the other hand, a goalie is not as likely to have prepped for not seen a defender attempt to score all game. Thus defenders have a surprise factor in their favor.

That’s counterintuitive. Where’s the data showing this?