The photographer has very limited availability to work with you.
First, keep in mind that this may very well be true. Or it may be true one week, but not the next.
The general idea of using limited availability as a photographer marketing tactic is that it can make a photographer appear as if they are in high demand. Items that appear to be in high demand are often viewed as superior to others.
Another thing having limited availability does is create “scarcity”. People tend to want things more when they’re more difficult to get.
In the end, be careful not to be manipulated to working with a photographer simply because you perceive them to have limited availability.
Make sure that you look at their work and have a good idea of what you can expect if you work with them. And if that is something you want, go for it.