Another factor is that no one is buying genset locos anymore. Several of the Class I roads have already sold or scrapped theirs, and smaller roads were never really buying them in the first place. This means there's much less demand for 4-axle locomotive frames and trucks to be used as genset fodder.
If the genset market was still booming, that's where a lot of these dead PAR GP40s would likely end up.
There's a glut of six-axle locomotives available on the used market right now, and a shortage of four-axle locomotives. Shortline and small regional railroads, if they're in a position to be buying locomotives right now, want four-axle locomotives. But they want ones that work, not ones that have been picked clean of usable parts.
Pan Am Railways — Boston & Maine/Maine Central — Delaware & Hudson
Central Maine & Quebec/Montreal, Maine & Atlantic/Bangor & Aroostook
Providence & Worcester — New England — GE Locomotives