I knew it. I fucking knew it. The moment I saw "payment system," I immediately jumped to the comments to find the EA and microtransaction memes. And I was not disappointed. 😂😂🤣🤣
Seriously, though -- it's obvious why the system is in place. The manga's premise is that this game helps him get his life together, so by making it (partially) P2W, it incentives him to seek out employment the more attached and invested he becomes in the fates of the NPCs.