So, it seems Twitter is the only platform where you can't get flagged for showing a nude human body.
To be fair, it's complicated at Twitter:
It's been a polarizing issue on my motorcycle forum forever. We don't allow nudity, however some people find ways to post images that cause a lot of heads to explode.
Ethan Zuckerman credits the rise of Mastodon as having to do with Twitter's media policy: