I'm going to take a wild guess and say you don't really care that much about the purpose of your software. You're not a game developer who's been an avid gamer since age 4, or a silicon valley entrepreneur who truly believes their web app is going to change the world. You've identified a niche that's liable to make some money, and are diligently plugging away at an implementation.

Your lack of inherent motivation from the product domain means you don't get any satisfaction from just getting the requirements met, so you hunger for the satisfaction of making a beautiful architecture. But all architectures have flaws. As a competent engineer, you notice the flaws in whatever you design, so your only source of satisfaction is compromised.

I would try to find work on a problem that excites you. When you get that giddy rush just from seeing your program give a correct answer. I think most software developers have felt this way about some project during their learning process. Look back and try to remember where it happened for you.

You're in trouble if software craftsmanship is your only source of motivation. It's a great motivator, but it is not enough by itself to carry you through a big project.

Now that you're in this project, it may be impossible to quit. I would find a side project to work on that provides more satisfaction. That should make it easier to plug-n-chug away at your current project without becoming depressed at the inevitable small failures in elegance and design.

I've never understood how developers can be happy writing CRUD apps or wiring together a bunch of pieces made by someone else. You gotta search for meaning. Even if you take a pay cut, it's worth it to find work that you care about.