IMHO, a B&B is different from a bakery. A B&B is a place of public accommodation, but a bakery is not, and should be able to refuse service to anyone, for any reason.
A bakery might be liable for discrimination charges if they are also a restaurant....that is, they serve food and/or drink for consumption on the premises.
Finding for the plaintiffs in this one would have risked undermining the Civil Rights Act of 1964. That’s why they won’t go near it.
Also, the bakery did not refuse to sell them a cake. They refused to decorate the cake in the way the customer asked.