Even for a free account, there is a contract in place between you and Twitter, which Twitter can't unilaterally terminate without reason, especially if the "code of conduct" collides with the right of free speech (https://www.ratgeberrecht.eu/internetrecht-aktuell/meinungsf...)

In Europe, GDPR has provisions about algorithmic decision-making, including a "Right to explanation":

https://turkishlawblog.com/read/article/221/algorithms-meet-...

I look forward to this getting used against Google and everyone else banning customers without explanation and/or recourse.

Property might be the wrong word here. I suspect that you do have a contract of sorts with any company with whom you have a free account. The consideration is sharing your data in exchange for the account.