I probably should have explained a bit more in depth about why I'm calling it a failure:
I'm simply not interested in the product I built anymore. Inventory for small businesses is something that doesn't hold my attention as it used to when I built the product, and I'm not sure it ever did.
Right now it's hard for me to load up my IDE and start working on the product. I feel like I don't know what to do with it as it is, and that stems from the lack of interest.
I'm taking a couple weeks to go over my options, and I think I've got a decent plan to revitalize it.
I haven't given up on the product itself, or the core problem it solves (inventory management). I've only given up on who it's marketed to.
Like you said, I think the best option is to change to a smaller niche. The one I have in mind will radically change how the product looks and functions, but it will still be inventory management.