The appeal I imagined for a particular type of person was the promise of sovereignity.

It's very difficult to bootstrap a new state on Earth. The failure of seasteading initiatives suggests land is a requirement for credibility, but virtually all land is either claimed or considered not viable (i. e. Bir Tawil).

But other planets offer new land that you could prop a flag on and potentially get existing states to acknowledge. You can set up a captive legal system, potentially find a way to domicile your paper wealth there, and potentially blow out the airlock of anyone who dares question you.

It's not that someone wants to be king OF MARS, they want to be KING of Mars.

There are places on Earth that are probably 3-5 orders of magnitude less terrible than Mars, and we don't even have a reason to colonize those areas. Let alone a cold, barren, lifeless, radiation-covered, nearly atmosphere-less rock.