Well, first of all, yeah actually it looks like the steam version was promised for free.
But I understand that the creator was not able to give out the key to everyone
Which is why people are asking for a refund because the key was promised and now because that is no longer true people want their money back. Plus considering not everyone can get a refund it actually is unfair.
While I understand the creator has said that they're basically different games. They do not seem that way to a lot of people. Yes there are differences between both, GUI wise, Feature wise, and more, but they're both being called by the same name which is why a lot of people are going to be thinking they're the same game.
Not only that but the creator claiming that the itch.io is a complete version but then also making impossible to buy it here doesn't make sense.
If this version is a different game then why isn't it available anymore but the steam version is?