Exchanges aren't doing anything illegal, nor wrong here. It would be like suing a butcher because he doesn't sell horse meat. If a butcher only sells beef, that's his choice, and you're free to go to another to another butcher if you want some other meat.

Regarding fiat currencies now, within the Euro zone, it's pretty easy to exchange US dollars or Swiss francs, but it's much harder to sell Hungarian forints or Canadian dollars. Again, there's nothing illegal nor wrong.