Because they're sovereign and the government doesn't have jurisdiction over them.
The ones I've known don't bother with driver's licenses, vehicle registration, or income taxes. They call themselves 'sovereign citizens' as if they are their own government.
And when they run afoul of that other government, the one that the rest of us grudgingly adhere to, things get interesting and sometimes violent.
One of my coworkers bought into the sovereign citizen idea that income taxes didn't apply to him and he improved his standard of living during the years that he escaped the notice of the IRS. When they caught up with him his lifestyle took a turn for the worse. But at least he wasn't violent and didn't add that to his problems.