But there's also less of a reason for anyone with permission to read DMs @ Twitter to do so, possibly with logging for any audits into unauthorized access. For mastodon, chances are your instance is focused around some general interest and thus getting on an admin's bad side could mean abusing their power to extract personal information/DMs from your account.

The only real issue with this wrt Twitter is that such failure of their internal employee auth allows malicious attackers to access DMs as well: https://techcrunch.com/2020/07/22/twitter-admits-hackers-acc...