It's not pettiness, its just business. They want the lock in, they want the ad views they want the user data. Don't anthropomorphize your lawnmower.
1. Using Apple Maps makes the switching cost to other devices (that don't have Apple Maps) higher.
2. Having more users makes any future monetization more valuable. I understand that there doesn't yet appear to be any direct monetization but I very much expect to see it at some point.
3. Removing traffic from competitors hurts them making their product relatively better the the competitors.
Same thing with Apple operating iMessage for free without ads... they don't care about monetizing iMessage but it's also not about altruism.