The reason for being able to see lists by the other classifications is because it's the same way that tournaments are frequently divided. Beyond having rating sections in tournaments there are generally also events that are only open to people below a certain age (or seniors events for players above a minimum age), or only to females. Females are also granted certain female only titles. For instance Hou Yifan holds the title of Grandmaster as well as the title of Female Grandmaster. The latter having substantially easier requirements.
To be clear, these divisions are all completely undirectional. Females, young, and old players can compete in any event and be rated against any player. Hou Yifan is regularly invited to top level events. For instance this year she was invited and competed in both Tata Steel and the Granke Classic closed events, competing against players including Magnus Carlsen and Fabiano Caruana. She scored a total of 0 wins, 10 losses, and 12 draws.