Electrolytic capacitors have shelf life, used or not. No doubt heat plays a role in their demise, but even sitting new on a shelf will eventually make a difference. It is the gel used inside of them that will eventually change with time. Just physics.
I had a PS Audio P500 which was still working, BUT some of the power caps were so dry they rattled. In this case, they weren't so old, but in heat environment that took their lives.