Why is Polkadot not a security?

Could you please explain why Polkadot is not considered a security? I've heard some discussions about the classification of cryptocurrencies, and I'm curious to know how Polkadot fits into this landscape. It seems to have certain characteristics that might lead people to categorize it as a security, but I'm not entirely sure. Could you clarify this for me? I'd appreciate it if you could provide a detailed analysis of Polkadot's structure, functionality, and regulatory considerations that justify its non-security status. Thank you in advance for your assistance.