I think that, for people beyond a certain threshold on the path to suicide, putting them in a situation where basic needs are not as readily fulfilled, and where death is prevalent and imminent... is a GOOD option.
Suicide rates are the highest in the happiest countries. One hypothesis is that sad people constantly surrounded by happy people are driven to remove themselves from society. Bill might have fit well in that kind of new environment. Presumably, he was anhedonic, so giving up the comforts of the West would not have been such a shock.
The point would not be to encourage comparisons with others' circumstances, and realize "how good he has it". Such comparisons are worthless anyway, as someone with worse circumstances might be at peace, while someone much better off might be in the same kind of turmoil.
Rather, going to such a place would allow for picking up coping strategies while removing certain pressures. People in America have an unaccepting attitude towards tragedy, and this may have made Bill Zeller feel like an outcast. We're all constantly force-fed an image of health, wealth, and well-being. It's hard to forget that this was not the set point for most human beings in history. Life can be gruesome in ways that are hard to imagine, and we are insulated from that.
There are countries where it's OK to have negative circumstances, and it's OK to be sidelined by them. If I had my arm amputated tomorrow, my social life would be significantly disrupted. If lived in a place like India, my missing limb would make much less of a difference.
And 3 months is not a long time to wait, if you've been miserable for 27 years. According to the original suggestion, no one would be trying to talk you out of it. He would still be free to kill himself, preserving his right to die in a manner of his choosing.