Look at this less abridged version of a quote already mentioned in this thread from an article on The Ambient:
“Moving forward, partners are no longer going to be able to access specific Nest data," Mike Soucie, Senior Product Marketing Manager at Google, and co-founder of Revolve (the smart home hub bought by Nest and shut down in 2015) tells The Ambient. "They're going to have to rely on the Works with Google Assistant platform to create routines with Nest products."
The reasons for this are security and simplicity, according to Soucie. WWN allowed many partners to access data about Nest products that today Google doesn’t feel they should have access to. These include Home/Away data, motion, and temperature set points from its thermostat, and the ability to turn on and off Nest Cameras based on external events.
“That’s sensitive data that we need to be sure we understand what partners are using it for,” says Soucie. “As much value as this is provided in the past it's been a bridge solution. I use the example of, you can't have multiple masters in the home, there's too many ecosystems today.”
Instead of having individual third-party devices control the same product, Google wants to be your smart home’s master. “What we were finding is that multiple ecosystems and multiple masters were trying to control the same Nest device. And there was a level of confusion,” he says. “Now, rather than having multiple platforms and ecosystems control Nest devices, we're bringing it all under the Works with Google Assistant ecosystem, a single controller for all your Nest, Google, and third-party devices.”
(Boldfaced emphasis added by me)
Yep, that's right. Voice control and routines is what we get. No cross-device automations. No access to your own detailed personal data.
These quotes from Soucie are evidence of Google's totally contradictory PR spin, including that carefully-worded response on Twitter.