I don't know about other states, but in Michigan, license plates are made by prison inmates, not by paid employees.
I don't have a problem with specialty plates to raise funds for state colleges/universities or for specific, non-political causes like Veteren's services.
I have a standard plate. It will eventually need to be replaced, but at the time I got this one, the standard plate had the image of the Mackinac Bridge on it, so I like it. They generally hold up for about 10 years before the rust gets them.
SC has 148 specialty plate choices. There has to be a staff to administer the speciality plate program which includes maintaining a website. With a government staff comes a budget and a bureaucracy all of which ends up costing taxpayers. Also, prisoners don't work for free. They might not get paid much but they're getting paid and there has to be a staff to manage the payroll.
BTW, Michigan prisoners get paid to make plates which means they are essentially paid employees. Wouldn't surprise me to find out that they have a fuggin union....................