In this industry, as in any other industry, as in boards - people come and go. You can model one day and the next assignment just doesnt come through. There are many fitness, figure and models taking on various photo shoots and gooing to various events for a limited time, then do a variety of other jobs. It is the same way in the guys.
And if one chooses not to persue other modeling jobs or photo shoots, and stay out of the limelight, that is their choice.