The Ingress game was a thinly-veiled way to fill in location data where Google didn't have coverage in it's own database, right? Why would they let this strategic asset go? I bet Mozilla MLS would love to have this kind of popular data source.
It's like how DNS queries to 8.8.8.8 can allow Google to find more of the web to spider.
I suspect Niamtic have found all the low hanging fruit, thus no more Seer badges.
It is also possible that Google has refined a "find local points of interest" algorithm which is based on where people stop for longer than might be indicated by traffic lights, pedestrian crossings or other signifiers. Then there is metadata from images (crawl places like Flickr and SmugMug for example).
Add to that the cost of having people review portal submissions and you can invent reasons why Google would want to let Niantic go.
Google will still remain as a "partner," whatever that means. But with this move they could try selling their location data to other players - Microsoft, Nokia, etc.
Nothing clear-cut, sorry. Although their policy does say they permanently log all requested domains.
Anecdotally, i run a private community site on "foo".dyndns.org with no inbound links anywhere, never submitted to google webmaster tools, but it shows up in a google search for "foo". Google public DNS is widely used amongst community members.
I haven't seen any links but I wouldn't be surprised. It was a theme (meme?) at Google to create a free service to generate data for other stuff. They create their 411 service to collect voice recognition information (for example). And I do believe Ingress (game) was originally a way to augment their maps data.
It's like how DNS queries to 8.8.8.8 can allow Google to find more of the web to spider.