See: https://news.ycombinator.com/item?id=27192997 (no one could actually tell which where legit and which were not)
It's possible that things have changed since I created my account nearly a decade ago, or that somehow I got a pass because google manages my domain's email. But they definitely do not force @gmail.com addresses for all devs.
EDIT: See this Microsoft extension [1] for example. It shows @microsoft.com, which is undoubtedly not managed by google like my little old startup's email is!
1: https://chrome.google.com/webstore/detail/microsoft-editor-s...
All the counter-examples I could find in the linked thread are Google Mail (for Business), which is functionally the same as requiring a gmail account in that it requires Google to be your mail-provider.
A lot of people in corporations set things up without necessarily understanding what they're setting up. This includes apps. If you're thinking, "Wouldn't Microsoft know how to set things up correctly?" the answer is "Not necessarily". It's not "Microsoft" setting up some app account, it's a random guy on a random team somewhere in Microsoft, who might not have ever published an app before, much less gotten any training or done much investigation into it.
You need to go to any google signin page, click "Create account" > "For myself" > "Use my current email instead".
You can then use that to make chrome extensions.
But this is how misinformation spreads. Many people only read it and believe it without looking closer.
We just trust that other people know what they are talking about. :)
... Also I could be wrong, I'm trusting the counter examples in that thread. :D