It comes down to bottom line pricing. Going with Apple Maps may cost Facebook et al. less than $0.30 per 10,000 polls, but when you think of how many people use location maps or pinpoint to find a place near them, it adds up fast. My understanding of IG's location is limited, but if it's merely showing near static imagery of an area with a pinpoint of where your geolocation tagged image is or a place you're looking for via their business profile, then it's a no brainer to go with a lower cost service.