Here’s how I would put it: I started because I loved the idea, my characters, the plot—I kept going because even though I have very little supporters, little is better than none.
Even if I had only one supporter that truly loved my work, I’d keep going for them. I don’t quit because people don’t like it. I’d quit because I don’t like the plot anymore, or I feel unmotivated—and even then, if I’m already chapters in, and I have some readers, I’ll keep going for them.
Really, it’s not a question of why, but how. How do you keep motivated, inspired, and interested? And even then, does the question really need to be answered?