Trope: Police have to keep bad guy talking on the phone long enough to trace them and find their location. Professional bad guys hang up right before it triangulates their coordinates.
Apparently, Hollywood’s been getting this inspiration from a pre-digital age when they use this trope in movies. See link for more info. It’s just funny that most of the “tracing the call” scenes I’ve seen are definitely after the 2000’s.
Another link: https://slate.com/news-and-politics/2002/10/how-hard-would-it-be-to-trace-the-sniper-s-phone-calls.html
A fun gif: https://i.gifer.com/9QtC.mp4
btw, on old POTS lines, your call is connected way way before anyone ever picks up. The audio can be recorded basically the instant the number is dialed. We used to do this at an old customer service training facility.
We’d hear people beating their wives in the background, screaming at their kids, etc. It was bad.