When you use a credit card to make a purchase in a store, the merchant pays the cc service fee. However, the IRS is forbidden by law to pay this, so they (not TT) must charge you when you use a cc to pay your taxes.
Turbotax does not charge a service charge to use a credit card to pay TT fees.
https://www.irs.gov/payments/pay-taxes-by-credit-or-debit-card
