This is a project in development.
That's why we have a Patreon, to support its development and that's why the prices for Shuggerlain here are the same as in Patreon (otherwise it would be unfair for our patrons).
So basically you are not paying for a game, or for the update of the game. You are supporting the development of this project.
If you don't want to pay more than once, you just need to wait until the game is finished. As we are doing with Space Paws. Well, now that I think, Space Paws is totally free and finished. I don't think that's something scammers would do :)
You probably paid 2$ for the previous update, but I can tell you the hard work we're pouring on this project is worth more than that.
Good :) We appreciate any kind of support to develop the game. We know nobody likes paying more or paying twice for the "same" thing (it's not the same thing, there is always new content and the new content always requires work) .
That's why we try to offer different options, and the player decides which is better for him :)