This website was envisioned soon after the obamacare fiasco which proved that the government is incapable of building websites. They felt they had no choice but using an outside contractor.
And, at the local (say town) level that's probably true. So what happens is they farm it out to an existing service for "free" and the service tacks on a fee. As a result, I either write a physical check or have my bank do so for town fees because if I paid directly online I'd pay a surcharge.