I'm in a totally different field, but I just finished a PhD, and I'm currently in a two-year postdoc.
Why did you get a PhD? You said you already worked as a software developer before, so it's not like you went straight through school because you didn't know what else to do. You also said your thesis was on a technical topic without practical application, so it doesn't sound like you were aiming for a non-academic job.
What kind of job did you want when you started? An academic job, then changed your mind? If so, you will have to be very intentional about selling yourself to employers. Frame the PhD as giving you experience in how to do research. It's going to be the rare employer who actually cares about what you did specifically.
It sounds like you are just firing off online job applications. Have you networked? Does anyone from your department know folks in industry? Did you apply for postdoctoral positions, research fellowships, etc.? If you are just looking at standard development positions, you are probably going to be rejected as being overqualified.