For the same reason cars have both locks and lo-jack, lol; redundancy only adds to the effectiveness.
Not to mention that relying on bike locks would be a silly thing to do in a city like, say, NYC. I've had $200 bikes stolen, despite having locks that cost almost half that. eBikes are in the thousands of dollars and theives use angle grinders.
Also, widely-known tracking software itself would be a deterrent if most brands started offering it or partnered with companies like Apple. I doubt the dude in this video would have stolen the bike if he'd known it had an AirTag on it, resulting in his immediate arrest.
This video is extremely clear evidence of why someone would want tracking GPS on their bike.