It's even simpler than that: Allowing others to dictate the terms of interacting with users would be very bad for Googles bottom line. What happens to Google Maps dominance without knowing who's going where (for new/closed shops) and how fast (for traffic information)? What about Chrome pushing users to install on desktop, Photos being built-in, and basically every other Google property being the built-in default? Android reports so much information it means Google will, IMO, always and forever have an edge over every other advertising company.