Privacy

Early iPhones all had unique UDIDs that were SDK accessible. It wasn't long before it was used to connect location data to devices and devices with specific users. Apple's solution was to yank it away from developers and go with an identifier the users could rescind and reset (the ADID). It still let apps track people, but there was always the risk users would reset it and break the chain of data gathering.

The real solution is to limit access to the information as-needed. Like for maintenance, or warranty repairs. Everybody else can go pound sand. In the desktop/laptop world, a lot of hardware vendors just blithely let anyone access unique hardware IDs, which leads to the same privacy outcome.