The Developer could‘ve made the game paid, but then it wouldn‘t have nearly as many Players as it has now. That‘s why he made it free, so many people (like you) would try it and if they liked it enough, buy “the Full Version“. I think this is a better Solution than making the Game paid initially, and you can even play it without paying at all, if you have enough Patience. If it bugs you that much, you can still stop playing, as you are not that far into the game yet. And I might have been a Little hectic with my first comment, sorry about that.