I wouldn't want the "average" new sofa either, especially not in a price bracket I consider reasonable.

I agree that it would be more efficient if people kept their sofas for a decade, but they don't, and me buying the sofas they don't want is a better option than them ending up on a trash heap. Plus, I'll probably keep them for ten years. I buy high-end furniture second-hand so I can do exactly that, rather than getting a new Ikea piece of junk that falls apart in a couple of years.

I suppose the ideal scenario would be for manufacturers not to make rubbish and for people to be able to afford good furniture that lasts for decades, but we don't live in that world.