Why is a 1981 D penny rare?

Could you elaborate on the rarity of the 1981 D penny? It seems intriguing given its seemingly ordinary year of mintage. Is it due to a limited production run? Or perhaps a unique design feature? I'm curious to know if there's a particular story or event surrounding this coin that contributes to its rarity. Are there any documented instances of its scarcity, or is it more of a collector's perception? Additionally, how does its rarity compare to other coins from the same era? I'd appreciate any insights you can provide on this fascinating topic.