Yes, the merchant fees are higher (or they think they are higher).
I have paid with American Express using contactless when the cashier insisted that they did not accept it.
I know the merchant fees are considerably higher for AMEX over say Visa/MC.
With this in mind, why would they even accept it if they aren't willing to say that they accept it (or allow people to use it)?
If you won't allow your employees to let people use it, perhaps you just shouldn't be accepting it at all.