The beer companies have freedom of association, too. The government cannot force the parade organizers to let gay organizations march, but other people can criticize the parade organizers for that decision. The beer companies can sponsor the parade or not, as they choose. Customers can buy beer from those companies or boycott them, as they choose. Freedom of speech and association goes two ways.
You appear to be missing an important distinction here. The beer companies had long sponsored these parades and always made a nice amount of money in parade-related sales. They would not have chosen to drop their sponsorships under “normal” circumstances. They dropped because of intimidation from the radical homosexual activists, who are notorious for making real trouble for businesses that do not lick their boots with statements of “support.”
If you believe “freedom of association” comes at the end of a fascist pink fist, then I guess you’ll really enjoy the new Amerika.