They're used in a few episodes. But, sparingly. The office one was used in the 1st season to communicate with the state police. Possibly the squad car one, too. Barney is told to monitor the car radio in "The Legend of Barney Fife". One of Maudie Prickett & James Westerfield's kids grab it with "testing, testing" in "The Family Visit".

My thought is it was integral in a lot of episodes not to be able to communicate with Andy or Barney gone in the squad car. It would of tightened up loose ends that would of killed the comedic aspect of a scene. So the radios didn't exist, but they were right there.

Here's a link about the office 2-way radio system.
https://forums.qrz.com/index.php?threads/eico-transmitter-on-andy-griffith-show.592631/

If Mayberry can have its own sewage system- yet still rely on a switchboard operator for phone calls, it's not surprising that Andy and Barn can have two-way radios yet rarely if ever use them to communicate with each other!