Google normally suspends accounts (notification after suspension with no real info) for heavily reported spam, they will suspend a ton of accounts if your domain is sending a ton of spam, even if its not via g-suite directly. This may be the case are you sure your domain is secured?

I don't know how any of my accounts could have been sending spam. I don't send unsolicited email, and I forward messages from those other four accounts to my primary email account, so I hope I would have noticed a spam problem. But because I cannot log in to anything, and didn't get any information or notification from Google, I can't be sure, of course.

I am subscribed to a lot of mailing lists and I wonder if, given my low human outbound volume, whether gmail-generated "bad attachment" bounces could have resulted in this. But that seems unlikely. More likely is someone ran a query and decided I had too many emails or was using too much G Suite storage. I look forward to hearing any information at all from Google!