Why Do Authors Hire Ghostwriters Instead of Writing Themselves?

I’ve always been curious why do so many authors find ghostwriters for hire instead of writing their own books? At first, I thought it was just celebrities or busy businesspeople, but it seems like even regular authors do it too. Is it about saving time, or is writing just harder than it looks? I imagine not everyone has the skill or patience to turn their ideas into a full manuscript. Maybe ghostwriters help polish the message while keeping the original voice? If anyone has worked with one or knows someone who has, I’d love to hear your thoughts. Do you think it’s a smart move or does it take away from the authenticity of the book?