Yes, mainly because Steam doesn't allow me to give away more than 100 keys and those are not enough for everybody.
But, besides that, the steam game is not the same game that is on itch. I am doing almost everything from scratch and I added new stuff and improve the mechanics, the user interface, there will be more languages available and more.
The game on Steam will be launch with 40% discount for 7 days and it will have localize prices.