Inbox was obviously a place the gmail team used for experimentation and now they are folding it back in.
Besides you're making it sound like there was some huge cost involved in adopting or in abandoning Inbox, which there isn't.
HN is for curious humans to exchange thoughts in community. It's hard to imagine anything that undermines curiosity or community worse than this. We frequently ask users not to accuse each other of astroturfing or shilling without evidence, but when we do find evidence—and there's a lot of it in this case—we come down hard pretty quickly.
What was "obvious" about it? Here's how Google introduced it: "Inbox by Gmail is a new app from the Gmail team. Inbox is an organized place to get things done and get back to what matters. Bundles keep emails organized."
Do you see anything about it being an "experiment" to eventually throw away? Not to mention Gmail already had the Labs feature for experiments.
In fact, what 2 Google representatives had said at the time was:
""We hope, in the long run, that most of our users will be on Inbox." (Alex Gawley)
"We care deeply about Gmail and Gmail users, but in the long run, as we add more features to Inbox and respond to user feedback, we hope that everyone will want to use Inbox instead of Gmail. Ultimately, our users will decide." (Jason Cornwell, Inbox's lead designer)