Four year old hardware has almost zero value.
That statement made sense ten years ago, easily. Less now, though.
GPUs are holding value longer, for obvious reasons. But even a 5 year old PC or server will be out of warranty, full of NLA components, and will get pennies on the dollar of its original cost on the salvage market. Most businesses will have fully depreciated them and maybe expect to sell them for enough to cover the costs of disposal.
There are ways to salvage old machines even when there is 0 support left/available.