my hunch is this: there are certain cultures that don't like dogs, and they whined and complained until they got banned. these cultures have more market power than northern european culture, so they won and got to enforce their values on everybody else. these are the kinds of changes in culture that we're going to have to get used to, if we continue to allow competing cultures to invade and dominate us - which we seem to be happy to do.
while some legal action is probably justified in the long run, what i'd suggest for now is voting with your wallet and picking transit options that allow for pets, whether they're classified as "support animals" or not.
i'd rather ban hijabs than dogs, myself. but, i don't have the money to make those choices.