That's the crux of the whole thing. Unless damaged, you can use good wired headphones for a long, long time, so replacing them doesn't happen often. With bluetooth headphones, the various companies can string us along into buying new versions every couple of years, as battery life, bluetooth sound quality and other technical aspects improve.
That is true but it also shows that people today are more willing to move away from cords. I know I haven't used wired headphones in over 2 years and it's an absolute pleasure at the gym, running etc without a damn cord getting in the way.