It’s because of the rights that viki has to remove the Turkish series.
It’s hard and very expensive to get the license so there were just fan channels.
Like i remember once they said they are thinking of if they will try to get the license for Turkish dramas in future due the high costs. But i don’t know much either.
Look into this topic. I thought there was also a post from a viki staff member but i can’t find that topic right now.