Why would a doctor not have appointments available for almost an entire year?

Tried to schedule an initial visit with/ an endocrinologist. Receptionist said earliest appt would be August 2025. Looked for others on my insurance network. Called a different place and they said earliest appt is February 2025. Still, months away.

What would be a reason doctors/specialist have barely any open spots? I couldn’t imagine them having 300 patients just lining up at the door!