I have noticed that the music made my most artists/bands is terrific during their first few records, but eventually gets monotonous, boring or plain dull. It's not really about their age, though. Just that the quality of music drastically reduces after they have put out a few records. There are exceptions, but very few. What could be the reason?
This is true of many band but not all. One reason is that creativity peaks between ages 30 to 40 in most humans no matter if it be in the sciences, math, writing or music.
Radiohead is one of the first exceptions that comes to mind. They've come a long way since The Bends. NIN is also a very sweet exception. The Fragile is my favorite piece of work by them. While Neil Young petered out a bit ago him now being in his seventies he gave us much good music for many decades.
Of course I can't overlook David Bowie this week. His style changed drastically over the years. Frank Zappa is a god. Fiona Apple continues to churn out good music as does Adele, Modonna, Cher.
These people are rarities. In other fields such as Physics most peak around 40. They are still great minds but by your later years most your good stuff is behind you. You may be better than most but not better than your 30 or 40 year old self. Same goes with athletes.
I feel like some just get to stuck in their sound... There's a lack of capability or unwillingness to expand their sound and make any attempt at real growth. Ideas are played out to the point where they can produce anything original anymore...
Every musician has their own way of interpreting their instrument and how to play it. In time, I think many "hit their peak" and then just exhaust themselves.
Because they're just appealing to the current market. They dont do anything new or truly original. Older bands just did their own thing without trying to be popular, so they developed a loyal fanbase who followed them over the years. People now just listen to whatever is popular that week and the bands are nearly forgoten very quickly.
The main reason I've seen is that they have burned through all of their ideas. It's hard to talk about how hard your life is when you are making millions and are boning the fans. What's left that they can talk about that their fans can relate to?
I think this is because the original motive of a band is more about the music. Once they get successful, it revolves more around success and money. Takes the creativity right our of your sails. Bands are almost better off retiring at that point.
Unfortunately, for most people, success and comfort causes them to lose passion and drive.
Whether you think an artistic production is good is a function of it leading you just the right amount. It has to be familiar enough to be accessible and new enough to be interesting. If your tastes move at a different speed than the artists you either leave them behind and they become trite or they leave you behind and they become esoteric.