Why is travel agency the leader of tourism development?

Tourism is a commercial industry composed of resources and tourists. Tourist attractions are sightseeing and ornamental resources; Cars, planes, boats, etc. Are all traffic resources; Accommodation, shopping and entertainment are all service resources. They can directly form a business relationship with customers, but they can't directly control customers. Travel agency is the intermediary between the above two, the integrator and agent seller of various tourism resources, the provider of tourism information and the organizer of tourists, and plays a role in controlling the market operation in tourism, so it is the leader of tourism development.