Whereas if you pay $800 for the IKEA sofa every 5 years, you know you're actually getting what you're paying for.
Plus people move apartments, move houses, move cities. Sometimes every 5 years or even more often. The sofa that fit in the old apartment is too wide for the new one. Or the style that made sense in your prewar apartment looks silly in your modernist one. Or now you have kids and you need it to be stain-resistant. Or what felt like a cool trendy leather couch when you were 25 now looks tacky and vulgar to you when you're 34.
For a lot of people, a sofa that's a fifth the price, that lasts a fifth as long, isn't a bug -- it's a feature. Quite simply, your sofa needs change.