We'll have to agree to disagree. I think short of being faced with someone who is such a high suicide risk that he should be committed for his own safety, prosecutors have no special duty to treat possible suicide risks specially.
What I find odd is that you think it "incomprehensible" that anyone would disagree with you. I think lots of people would disagree with you on this point. Indeed, I think the majority of Americans would disagree with you. We put people in jail for stealing to feed their kids, we put people in jail for killing abusive husbands, etc. We go out of our way to treat defendants uniformly.