So like a lock? It's an arms race, and if these things did really take off, bike thieves would find a way to defeat them (easy enough to detect if a bike has one after all).
Also it's not as if many many iPhones aren't being swiped on the streets of London either.
A tracking device though would be embedded inside the frame itself, and thus not be removable without cutting up (and thus likely destroying) the frame. The frame is the single-most valuable component on a bike.
Depends. And parts can be fenced with much less risk than entire bikes. I doubt that trackers provide any actual safety improvement, neither in the small (what will you do with the information you might get?) nor in the big (will trackers eventually reduce the number of thieves?).
What might help, I think, are serial number registries. Rohloff hub serials can be registered by owners and checked by would-be buyers, which I think does have some of the desired effect of making those bikes less attractive to thieves.
Contrary to what the other commenter said, this is not attractive for carbon frame owners as I wasn't thinking GPS tracking, but low power, snitching networks (like Apple's stuff, where the stolen iPhone only needs to be seen by another iPhone; or like corona tracking). How often do you see a carbon bikes in the wild? A frame like that may also have other components worth destroying the frame over.
Bicycle frames have to be a lot stronger than phones and laptops. That means greater wall thickness (I think ½ mm is on the lower side for steel bicycle tubing)