It just feels....disrespectful to the original supporters. The original supports are likely why there was a big push to steam in the first place. Heck likely the reason the developer decided to put more content in the game. If the game got no support the developer would have likely just moved onto his next project/game. He got the financial backing from people buying a product on Itch.io because they wanted to support the game even though I bet it was very easy to pirate (I never checked but I can only imagine it was).
Like it just discourages people in the future to want to financially back products they like because the end result will be them getting left behind. I guess they get early access to the game? but now they have to make a second purchase just to get it on steam.In this case left behind refering to no multiplayer and updates coming later to itch game owners.
YES we can repurchase it. There might be a day I will re-purchase it. I'll still feel like its unjustfied however when I make that purchase.