So my initial theory was, hey, I guess I actually have more of a social life since then--a real social life with people here in the bay area, and also my expanded mud social life since I joined IFmud a month later--so I just don't have any time to spend on it. But in hindsight, that doesn't seem to be true--I recorded ten or more previously-written songs since then, and I've still been recording sketches of instrumental stuff in the last few months. I just haven't been writing any songs.
My last song was called The Perfect Song and was about being inspired by someone to write the perfect song, but the lyrics make clear that I didn't actually think that The Perfect Song was itself a perfect song, in that stereotypically smarmy self-deprecating way ("the bridge would be good too, but this one will have to do").
But, having retired the "I'm too busy" possibility, maybe it really was the perfect song and I shall never write another song again since I can't top it.