I write historical romance in the regency era because of Science Fiction Conventions.
When attending Science Fiction Conventions I discovered some people who read science fiction also enjoyed the works of Jane Austen and Georgette Heyer, like I did. So much so that they wore regency costumes at the convention. They even had regency dancing on the convention program.
These Science Fiction readers and writers knew a lot about the regency era. Intrigued, I did my own research on the era and quickly went from being a casual regency reader to a regency history buff. After that, it was just a small step to writing regencies.