I think the primary reason people lose their willingness to contribute is living in a situation that is both "unending famine" (from their perspective, not GDP)

I think the primary reason people lose their willingness to contribute is living in a situation that is both "unending famine" (from their perspective, not GDP) and "rivalrous" as opposed to "cooperative". Such a situation engenders sharp elbows and hoarding. But it reverses itself soon enough when either the "famine" ends or when cooperation is rewarded rather than stepped upon.