I think they are not that interested in selling the game as soon as possible on steam, or any platform as they are developing the game with their patrons.
So as a player I also want to play the final version as soon as possible. But as a patron I want them to take care of their product. I love Naisha's art and animations and I don't think it's something easy to replicate. Some games have different artists, that have different styles and to be honest, that doesn't look professional to me. So I prefer they keep doing as they currently are.
Also, I understand the steam thing, I mean, not sure of how much popular they will be there or how much they would sell. But as long as I know, steam takes the 30% of the sales, and another 20% in VAT. Patreon depending if you were founder or not takes 5-10% of the income. So to me, the steam thing would be more like a promotional move.
Anyway, they already announced there will be Steam version. And I don't think they will wait until the final release to publish something there.