What are the disadvantages of decentralized VPN?

Sure, here's a question that simulates the tone of a questioner while describing the disadvantages of a decentralized VPN: "As someone who's interested in using a VPN for enhanced security and privacy, I've been exploring the idea of a decentralized VPN. However, I've heard some concerns about potential disadvantages. Can you explain what some of the downsides of a decentralized VPN might be? For example, how does it compare to traditional centralized VPNs in terms of speed, reliability, and overall security? I'd appreciate any insights you can provide on this topic.