Given that the "point of principle" is not paying money, and that the "Sovereign Citizen" movement is heavily into tax evasion and dubious legal manoeuvring to get out of debts it seems very, very likely that greed is behind it.
I think it more likely that the "Sovereign Citizen" stupidity is behind the assertion that. Indy is being denied access to lawyers. It's entirely possible that that comes down to Bundy rejecting lawyers who give him sensible advice rather than going along with the crazy cargo cult law he prefers..