why songs don't show up in composer's discograph list ?

[RoJohn]

As you see in the picture below, this song has a singer and a composer. It's shown in singer's discograph page clearly.

However, if we turn to composer's discograph page, there is no sign of this track.

But I can still find it by searching the composer.

So here is the problem: why can't I see an artist's all tracks, including those he has contributed to, in his discograph list?