Because they don't actually worship satan, rather exist solely to highlight religious (especially christian, given them being US-based) hypocrisy. The name choice and theming around satanic symbols was probably done more to symbolize going against the reality of christianity than anything to do with christian myths about satan, as well as to specifically piss off those christians that go on about religious freedom but are against the satanic temple getting the same freedoms as the christian church.

The whole Satan thing is just a metaphor for acting against Christian Supremacism. They don’t actually believe in Satan.

TST is not theistic.

In addition to what others have said about the worship not really being genuine, in the Bible, the evil of Satan (whichever flavour that story is using) is mostly tied to his defiance of Yahweh. By definition, their god is everything that is good, therefore anything in opposition must be evil.

The only time he performs unambiguously evil acts is when God gives him permission to fuck with his just loyal follower, just to prove to Satan that he would still be loyal, which has them both looking bad.

Other examples of "evil acts" include encouraging humans to seek knowledge, encouraging David to perform a census, telling Jesus to try something else, "entering" Judas so he'd betray Jesus (which was also a necessary part of the whole Jesus salvation plan), accusing Joshua in front of God and being rebuked for it (which makes his whole timeline questionable because apparently he fell from heaven before humans were a thing but he's there to accuse Joshua so Yahweh can rebuke him and reestablish Joshua's legitimacy in a time when his grip on his spiritual power was tenuous).

Because of all of this, there is a school of thought that says, if the characters and events in the Bible are real, maybe the whole thing has been a smear campaign against Satan because once you drop the whole "defying Yahweh is evil" assumption, Satan's record looks a lot better than Yahweh's.

But the more I look in to the Bible, the more it looks like a transparent power grab and hold. Which was specifically the reason Constantine adopted Christianity for Rome, because he was having a hard time convincing people in Iberia and Gaul they should be fighting wars in Anatolia and the Middle East and wanted to use religion to give a common identity.