Because freedom ain't free... literally
"No state shall convert a liberty into a license, and charge a fee therefore."(Murdock v. Pennsylvania, 319 U.S. 105)
"If the State converts a right (liberty) into a privilege, the citizen can ignore the license and fee and engage in the right (liberty) with impunity."(Shuttlesworth v. City of Birmingham, Alabama, 373 U.S. 262)