It's just a bit of historical cruft. A long time ago, games were an optional part of the system, and might be installed by different people, so they lived in
/usr/games rather than
/usr/bin. Data such as high scores came to live in
/var/games. As time went by, people variously put variable game data in
/var/games/NAME and static game data in
/usr/lib/games/NAME (and the same with
share instead of
lib for architecture-independent data). Nowadays, there isn't any compelling reason to keep games separate, it's just a matter of tradition.