Why do coin collectors want to collect money?

Could you elaborate on the motivations behind coin collectors' desire to accumulate various forms of currency? Are they driven by a passion for history, the allure of rarity, or perhaps the potential for financial gain? Is there a specific type of coin that tends to be more sought-after than others, and if so, what factors contribute to its desirability? Additionally, how does the process of collecting coins differ from other forms of collecting, and what unique challenges or rewards does it offer?