It’s also because Google Accounts is such a complicated mess by now that no one inside Google knows how it works: https://grumpy.website/post/0PU1U2r3v
Tell that to someone using G Suites! I don't know the real internal structure, but I've experienced a frustrating number of "unsupported features" or "unexpected errors."
Those UX complaints wouldn't exist if Google Accounts were as internally unified as you make them out to be. With a unified set of internal tools and APIs for teams to work with and make sure their product works.
Meanwhile, it took YouTube more than ten years to be able to support not just the default user. BigQuery is 9 years this year, and can't support multiple users in the browser etc. etc.
It gets worse than that.
Because they are still kinda unified. You get blocked for whatever reason on YouTube? Oh. Say goodbye to the rest of Google properties: play store, your dev account etc.
Actually, compared to all of my other gripes with Google services, I've always found their account management to be pretty coherent and easy to understand lately.
SSO on iOS across the browser and Google's native apps, and "sign in with Google" in 3rd party apps, works flawlessly for me.
The only thing I'm missing is a "sign me out" button (per device or even on all devices) that actually works.
As a person who uses at least two accounts (personal and work), and a third account on YouTube (I've had it since before Google Accounts), the number of Littles things that way consistently don't work is baffling. Well, you can see just one day's worth at the link :)
