Lower end cheaper carpet lasts up to 5 years before needing replaced while more expensive carpet can last from 10 to 15 years.
Even 10 years is a pretty long time for carpet and after 10 years I'm in the mood for an update to my home and sometimes sooner so I replace the carpet in my bedrooms and living room just for that fact.
After 10 years the carpet has given me my moneys worth anyway.