Do they all up and out say they don't like gay people? do they make you attend a celebration of not liking gay people?
It might, at first glance, to be merely semantic, but you keep saying wedding vendors are forced to "attend" same sex weddings. There is a difference between 'attending' a wedding and 'working' a wedding. The vendors are just plying their trade. They are not required, nor requested to approve of the happy couple.
Could a restaurantuer refuse service to a walki in four top of homosexuals? I wonder what that restaurantuer's attitude might be on a slow Tuesday night? But the maitre d does not sidle up to the table, the sommelier doesn't bring an extra glass and make a toast.
And wedding vendors, with the exception of the waiters and bartenders and musical entertainment should be invisible. It's the bride's day, not the day for a vendor to grant his empremator even on the occasion.