Although I consider myself in many respects a generalist writer, I've been reminded recently why specializing makes a lot of sense.
When I decided to start an association specifically for ghostwriters, I turned for guidance to an expert in the field. I wanted to get up-to-speed quickly on how to structure such an organization, how to best serve ghostwriters, how to connect with them, etc. and knew this knowledgeable guru could help. And she did. She had years of experience in starting several of her own membership groups and was extremely helpful - because she was a specialist in this area.
However, I've noticed in the last few months that she has shifted away from teaching others how to start membership organizations, like associations, and more toward teaching women how to start and run companies. She's gone from targeting a niche audience to targeting a broad cross-section of women. Which is fine but, in expanding her focus, she's become less useful to me.
I suspect that potential clients may view ghostwriters with the same filter. If they want help writing a memoir, they will likely search for a writer who has previously written memoirs. Or should a CEO decide to share her tips for success, she may go hunting for a writer with an MBA. Not that a skilled writer couldn't tell her story just as well but, that a writer with business training much like her own will speak the same language. That's a big benefit of working with a topic specialist.
If you agree and think you're not being as aggressive as you could be in highlighting your own specialist talents, I'd suggest a few things. Make sure your social media bios include keywords related to your expertise. Mention articles you've written in that area, companies you've worked with and projects underway in that niche. Post blog mentions of tips you've picked up in your specialty.
In sum, make it much easier for potential clients to come across you when they do their own search for a specialist. Then demonstrate that you are one.