Reasonable points. However the majority of devices which access the Web already have a mapping app built in.
Developers already have to do the dance of signing up for API keys, this redistributes the work back to browsers.
And, as I hope I made clear (but possibly didn’t) this wouldn’t stop developers from using whichever mapping provider they wanted. They can still pull in 3rd party maps – just the same as they can do for video or audio.