They don't. LEOs will routinely conduct searches without any warrant or probable cause and if they find anything and the defense tries to have it thrown out, the LEO will say the search was "voluntary". Similarly, they will say people were "voluntarily detained" if they don;t know to ask "am I free to go?"

Calling yourself a sovereign citizen will get you nowhere. Saying "I don't consent to this search" will not prevent a search. But it will allow you to get anything found suppressed, unless a judge decides there was probably cause or the body cam happens to fail and so there is no record of your refusal.

> why would law enforcement and courts go along with it?

They don't want to deal with it. If someone has one of those SovCit license plates, you know pulling them over is guaranteed to result in frustrating verbal sparring match, which may result in the cop giving up (which is then shared as evidence for the SovCit movement's effectiveness!), or may escalate to a physical altercation.

Whether or not the SovCit practitioners understand that's what's happening is anyone's guess.

> Like, why would this be true

Steel-manning the sovereign citizens movement (which I don't believe in): they believe authority comes from the consent of the populace, which is a true statement and in many countries founding documents, they mistakenly think that means the law doesn't apply to them when they as an individual do not consent.

They basically don't get that democracy is the tyranny of the many.