How long do the cushions on budget outdoor sofas last?

Across r/patio and r/homeowners, the recurring theme is that cushions are effectively consumable. Owners report olefin and foam cushions often start to flatten or look tired in roughly three to five years even when the frame is still solid. Reviewers widely recommend budgeting for a cover or covered storage, and several note Sunbrella fabric holds up better than generic olefin if you can find it.