There are a few reasons that this may happen but all are easy fixes. 

Firstly, when configuring your packages, you must assign qualified photographers to each package, ensuring they will show up as available. To assign a photographer as qualified, you must go in to the Package Configuration, and within Pricing Strategy, click the button on the left of the task, under Qualified Users. Here you can select which of your photographers can be assigned to each task. This selection can be made for every package as well as individual add-on services. 

Another factor in photographer assignment is coverage area. If a photographer does not have an assigned area, they will not be made available for scheduling. When setting up each user profile, you must designate a coverage area in which that photographer is active. Choose the area directly on the map to set up.