A VPN is a middleman that accepts your traffic and forwards it, hiding who you are to servers. An onion router is like a VPN but instead of 1 middleman, the middleman is a whole random network of middlemen, and those middlemen also hand off to other middlemen.
What I don’t get is why people don’t regard Onion Routers as a form of VPN. It’s still uses a virtual private network, just more of them. a network of networks.
Surely TOR is a type of VPN?
Maybe there’s some details I’m missing. I’m no expert
Really mostly convention. Yes you could label it that way, but people consider it to be enough of it's own thing to not do so. (+ there is some value in not conflating the two because they do have different threat models etc and users should treat them differently too)