You pay because you like the game and want to support it. You do that while knowing you're getting ripped off in the process, plus the possibility of getting even more burned in the end with something that is never completed. That's your choice. I would never do that, ever, because it's a complete waste of money for something that would have a real-world price of less than 20 bucks when finished.
If I ever support something on Patreon I do it at a $1 tier and if they don't have that I do a custom amount. IF, and it's a big if, the game get's completed then I do a one time pledge for the market value of a premium visual novel. By doing it that I have basically no risk and all the reward. If it doesn't get completed, then big deal.
Steam version does cost $15 and not 10, and the $15 patrons from what I can see did get the game before it released on Steam. You're making that decision to put up money every month to support something. Early adopters never win in the end. The guy who waits for a finished product and pays $20 or something for it wins. If it doesn't get completed, then who cares? because nothing came out of my pocket.