The US first amendment has nothing to do with what a private company chooses to host on their platform. That content is there because the users and owners of the platform want it to be there.

> The US first amendment has nothing to do with what a private company chooses to host on their platform.

The First Amendment (largely) prevents the government from choosing what a private company hosts on their platform for them.

A version of X hosted in Germany would look quite different.

In countries without the first amendment, private companies are required to block nazi content when they see it and ban nazis when they see them.