That's because they don't believe Satan or dark magic exists.

All religion is as meaningless as the meaning we attach to any word.

U.S. Christian Nationalists are engaged in a campaign of legal and political efforts to change U.S. law and public policy in such a way that it removes divisions between public policy and religious doctrine, or uses public money for Christian causes. The Temple of Satan was (at least partially) founded to combat those efforts and to set people free by spreading knowledge. They do this by subverting the laws that privilege Christians (religious holiday displays, religious after school clubs, etc); by working to shine a light on what Christian’s are doing while offering a community and guidelines for moral living without fear of gods concocted by prehistoric man. In many of their materials, they allude to being the snake in the garden of Eden, whose only crime was sharing information with Eve. In the one bit of research I did for this comment, I also learned that satan is just the Hebrew word for “accuser” - and originally they just pointed out how dumb some things were.

Contextually, the Temple of Satan name is honestly probably more relevant to them than Christian is to U.S. Jesus worshippers.

What do you think Satanism is about? I model my behavior on a rational, scientific, and humanistic worldview and I fight against superstition. One of the predominant superstitious organisations in my country have a mythical being that espouses all of these same traits and they call it Satan. It's convenient for us to refer to ourselves using their own language, so they instantly know we are against anti-humanism and superstitious oppression.