That's not been my experience. I've got plenty of 7+ year old machines and DC infrastructure components that are even older than that. Power and compute density improvements are no longer fast enough to have full turnovers in 3 years.
Big companies refresh based on their depreciation and not if they are still usable, these are usually fully depreciated in 3 - 5 companies, depending on their accountants. Also, there is going to be massive growth in DCs with AI, companies aren't going to compete on 7+ year old hardware just because it runs ok.
That's not been my experience. I've got plenty of 7+ year old machines and DC infrastructure components that are even older than that. Power and compute density improvements are no longer fast enough to have full turnovers in 3 years.