I doubt this has anything to do with my Unlimited Drive storage thing. Google are doing this to stop API consumers from storing user data on their own, presumably less safe than Google's, servers. I agree with that decision completely.
These scam apps trade off being inside the protected platforms, so users expand their trust assuming (incorrectly) that a third party app will treat their data well.
"This is how scammers are now abusing Google Calendar to pillage your data"
"Gmail app developers have been reading your emails"
The headlines are ALREADY happening.
Why should google risk their brand so some grow fast and break things startup can create the next cambridge analytica scandal? They are one big CA type scandal away from being looked at as the next facebook (not a good look).
To me, it reads like this: Google is going to prevent users from storing users' data elsewhere. As if it's Google's data, not users'. Though with the free tier this as well may in fact be the case :-/
I also imagine there is the other side where the third party has crap data security. End users figure that their data is safe with Google and may not consider that there is a third party with their various levels of security.
I can see Google copping a lot of heat should Company X have a data leak and that data was originally gathered from a users Google data store, whether it is justified or not.
It's going to be "Gmail data breached".