I'm preparing to start releasing all of our full games on Itch as well, but didn't want to release anything during sale season. I will start with our first game and work towards Building our Futature.
The reason for directing people to Steam is simply the way the Steam algorithm works. Wishlists are important and make Steam recommend the game to more people/in more places. I prefer Itch, but it's a lot smaller than Steam. I'm not in a position where I can afford to take the loss and ignore that.