GPUs don't really have six year lifespans, though. The hardware itself lasts far longer than that, even hardware that's been used for cryptomining in terrible makeshift setups is absolutely fine for reuse.
In three years the current generation of GPUs will be 50% or more faster. In six years your talking more than 100% faster. For the same energy costs.
If you're running a GPU data center on six year old GPUs, your cost to operate per sellable unit of work is double the cost of a competitor.
H100 to GB200 saw a 50x increase in efficiency, for example.
Nvidia only advertises 25x efficiency. And that is their word...
But the point is — you don’t decommission profit generators just because a competitor has a lower cost structure. You run things until it is more profitable for you to decommission them.