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 conventions. They even had regency dancing on the convention program. When the World Science Fiction Convention was in Brighton we toured the Pavilion in full regency regalia.
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.