Some of the most basic radios that came with TJs from the factory had no rear channel outputs for a sound bar. It's possible the PO installed the sound bar & gave up after possibly discovering the radio doesn't have rear-channel speaker outputs.
If your radio has a fader (not balance) control, it has rear-channel outputs. If there is no fader control, it doesn't. That's not to say you can't make the soundbar speakers work if it doesn't have rear speaker connectors. You can always wire the front and rear speakers in series with each other. That of course isn't optimal but it would work.