> (e) No Use With Non-Google Maps. Customer will not use the Google Maps Core Services in a Customer Application that contains a non-Google map. For example, Customer will not (i) display Places listings on a non-Google map, or (ii) display Street View imagery and non-Google maps in the same Customer Application.
As far as OSM goes, Apple Maps is based heavily on OSM data. (I've submitted corrections to OSM and seen the changes propagate to Apple Maps.) So I don't see much point in supporting two different services which are that closely related.
Apple does make some contributions back to OSM though for submitted corrections in areas that use OSM as a fallback, IIRC. Apple Maps unfortunately doesn't do a great job of mixing those results though and only uses them as "fallbacks". It's why some areas have poorer quality even compared to OSM (such as Germany mentioned in another comment) because they're strictly using their own data instead of using OSM, et al. to fill in the gaps.