There are plenty of reasons! Here are some of them:
Sad
Happy
In love
Angry
Hungry
Tired
Pensive
Insane
Bewildered
And so on
There you have it, any sort of emotion at all is just cause for song. It makes perfect sense.
If that were true, you could pull him out of his ship, pour lye all over his body, and shove a hot poker up his ass. Scratch the last part, he might like it...