Unlike dark fiber which retained value, GPUs and compute hardware rapidly becomes obsolete. It won't make sense to use anything more than 4 years old, as performance and especially energy efficiency will have improved in that time.

I wouldn't count on getting significant value out of the debris of the coming data center implosion.

Copper thieves are likely the only ones who might, but there will likely be a glut and the risk likely won't be worth it for even them.