Why is 1965 quarter so rare?

Could you elaborate on why the 1965 quarter is considered so rare? Is it due to its limited mintage? Or perhaps a special historical significance attached to that particular year? Are there any other factors, such as design changes or material shortages, that contributed to its scarcity? Understanding the rarity of this coin could help collectors appreciate its value and potential investment opportunities. Could you provide any insight into its current market value and whether it's a good addition to a coin collection?