Data does not belong to Google, it is licensed under certain conditions, which include unability for third parties to access raw data. Be those conditions continuously broken, Google will no longer be permitted to use the data, so not just no more Gaia, but no more Google Earth. That's absolutely not what I want, not I hope any of you want.
In essence, if Google allowed 3rd parties to manipulate data, it could lead to a loss of licensing, which would mean Google Earth would disappear. While it's unlikely that it would go that far, it seems both the head of the Gaia project and Google were amiable towards each other, and the project is being terminated under “friendly” conditions. The above link explains it in great detail, including correspondence between Google and Gaia.