This is such a good idea that a number of high-end bike manufacturers agree with you and do so. VanMoof is one example, but they are not the only ones.

I believe VanMoof mainly makes e-bikes - I was thinking more of high end carbon fibre road bikes from companies such as Specialized, Giant, Pinarello etc.

Maybe it's a weight-weenie thing as e-bikes are already heavy so adding 100g isn't noticeable (not that I'd be able to notice 100g on an acoustic bike).

My Van Moof bike has this, they even offer an additional service where they go and get the bike back for you

Does this service involve very large men all wearing black and ear pieces?

There was a post a while back from someone who did this for Van Moof. The majority of the time a simple "that bike was stolen, can you give it back" works just fine.

Something like an airtag would probably work.

Airtags and similar can work, but there are downsides. For one, AirTags specifically have a series of anti-stalker features. That means a thief knows the bike is being tracked. Second, any tracker you hide on the bike can be found by a thief and removed.

Having it integrated by the manufacturer means both avoiding Apple's measures and making it much harder to find and remove. So it's generally a preferable option when possible.

I think it would be hard to hide an airtag effectively on a metal-framed bike. Putting it in the frame would interfere with wireless communication and any other location would be easily discovered.

That's correct [1], but there are plenty of accessories to hide one pretty well still.

[1] https://www.youtube.com/watch?v=aLtWN1Mp2Qc

Cyclists can get incredibly OCD about weight, they will buy bolts from more expensive material to save tiny amounts of weight. Peron anally I always found this a bit strange as things like cutting your hair would likely save more weight.

I think the only problem I see with this is that most competent bike thieves are going to know what bikes include gps and how to remove/disable it (or to strip it for parts and ditch the frame)