The neighbor hung up, but the scammers didn't, and the call was not disconnected...

BeefWellington · on March 31, 2022

Yes, and this is how it works as another responder mentions.

The thinking by phone companies is essentially: guy calling pays for the call, so we can milk each call for a few extra cents each time even if they're shady or a wrong number.

afiori · on March 31, 2022

Apparently it is a feature Called Subscriber Held (CSH).

https://security.stackexchange.com/a/100342/143105

TL;DR It was just how analog phone worked, users came to rely on it, digital exchanges reimplemented it (with a timeout)