Can't speak for others - but, for me, it might be because when I'm feeling really happy, the last thing I want to do is figure out why so that I can write a song about it. smile

I might want to sing a song or whistle one. But not write one.

On the other hand, feeling sad or blue does seem to make me introspective - maybe so that I can figure out why and get out from underneath it.

Songwriting is therapy - and happy folks don't need therapy grin

The smart thing to do, I reckon, is to remember that feeling when you're really happy and write about it later, when the feeling has passed! smile

Problem with that, as Sam mentioned, is that it might seem forced - coming after the fact.

Scott