It's because people change.
Let me explain this as best I can. I have a rock band. We are good. As soon as we get stuff recorded it's going up on the board and we're going to make a demo CD and everything and try to get signed and play shows. We fucking slay.
When I first started writing songs for the band (I am the primary songwriter), I was about 19 years old and my longtime girlfriend had just left me for another woman and I was angsty and angry and dark. I wrote some real killer tunes. Real deep stuff, bordering on emo but much darker, very doomy. Early Sabbath shit, here.
Now, I have a fiancee, I'm going to be married in May. I've got a new job, my future is bright. Things are looking up. In short, I'm happy.
However, when I sit down to try to write a song, it is more often than not absolute shit. For every one song idea I stick with there are three or four songs that are absolute drivel, and if we ever put them on an album they'd be filler. I cannot write a song filled with bile and vitriol any more, because I no longer feel those things. My life makes me want to write about butterflies and puppies. I HATE music about happy things.
So what am I to do? I spent a long time thinking about this. In the end I asked myself, "What would Opeth do?" The answer, it seems to me, is write music that is not as angry but overwhelmingly artistic. I may not be an angry teenager but I can sure as hell make art like a motherfucker.
My point is, bands grow up, people change. This happened to Metallica. As they grew up, they became more mature, and success simply made them less angry at life and the government and other aspects of their previous works. Most bands experience this sort of change. Dee Snider, frontman for Twisted Sister, once said, "It's hard to make music about being an angsty teenager when you're sitting by the pool of your mansion next to your hot wife." Such is the paradox of success.
The same things don't mean as much to a 23 year old as they do to the same person at 33. The fact that they've used their good material may have something to do with it, but the simple fact remains that artists make art that is relevant to them and what is relevant to a musician one year may not be the same at another year, another album, another stage in his life.
Subsequently, those to whom the original or "better" material IS relevant will wonder, "what happened to this band/artist? why did they start to suck?" Indeed the overall quality of the music may have fallen, but farbeit for us to say that an artist's music sucks simply because he writes or plays about different subjects.
Except Metallica. They just suck now.
