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.