I think you’re referring to a different event (having an account suspended or banned) than the parent comment, who’s questioning the notion that one wouldn’t have a subscriber list in a CSV or Google Sheet outside of the account, and/or in the event that a service closes up shop, that they would not extend an effort to allow users to export their data.
That's still not answering the question though. I don't know of any bulk email provider who doesn't allow you to export and import your lists via an open format like csv.
> It's a general comment on the professionalism of the bulk email delivery industry, namely there is none.
I strongly disagree. I’ve had the chance to speak with numerous deliverability folks who work at esp’s over the years and they’ve all for the most part been incredibly professional and helpful.