They don’t have to turn it down because it’s gay. They can turn it down because they’re not interested. Pure and simply not interested
Sure, people can lie about their reasons for not wanting to do business with someone. It's an easy way out. But this company has chosen to pursue a more ethical path and make clear whom they wish to do business with and whom they do not. And the government is punishing them for that. Rather than encouraging dishonesty and punishing honesty I would prefer the government did the opposite.