Unwittingly, Monygham is hammering further nails into the coffin of Nostromo's allegiance: what Nostromo hears is, "Yes, your life was meaningless to all the rulers."
On a deeper level, the symbolism of "treasure" as inner worth or
character continues, with "surrendered this treasure" meaning "sacrificed
my integrity" (which is what Nostromo would have done by showing a light
to Sotillo). The doctor's grim remark implies that at this point of the novel,
all the characters have surrendered that, along with their ideals.