I got interested in learning how to TDD and how to write tests because I wanted to improve my overall skills as a developer.
I had this idea that there are too many technologies, and they change so fast that I can't learn all of them in-depth, so my countermeasure was to improve my testing skills. Tests will tell me if what I'm building is working or not. They will also give me feedback on the design of what I'm building. And all of this independently of the frameworks/tools I'm using. So even when I have to dig in a codebase that uses technologies that I'm not so familiar with, I'm always reasonably confident that by writing tests and by reading the technologies' documentation, that I can get productive pretty quickly.
What about you? What made you interested in learning how to write or learning how to TDD?