The reason: I am utterly opposed to any type of suicide.
90% of the time, suicide is--I believe--committed whilst the sufferer is temporarily unhappy, depressed, crazed. And it passes. It really does.
Likewise, 99.9999% of the time, assisted suicide is--I believe--incredibly selfish. My reason will become apparent below.
In terms of popular culture, below are three times that the assisted death actually works thematically and structurally.
1. Dexter. Camilla.
To follow the Code of Harry, Dexter gets files of evil criminals and takes out his homicidal needs on those criminals. The woman who runs the records office figures out Dexter's purpose. When she goes into the hospital with a terminal illness, she asks Dexter to take care of her. He does so using drugs in a pie that he feeds her.
2. The Mentalist. Coroner Steiner.
Steiner doesn't ask Patrick to kill him. Good people do not make this request. The woman in the records office can ask Dexter because Dexter is homicidal. But Patrick, for all his faults, is not.Killing someone hurts a person. It may sometimes be necessary. It is still an emotionally and psychologically devastating request that will change a character (as John says in Person of Interest, "Your sister gets to keep her memory of you [as you are]").
The coroner doesn't ask Patrick to administer the drugs. Rather, he wants someone to sit with him to testify to his intent, so he will not be autopsied. After some hesitation, Patrick agrees and even helps the man relax by using some of his carny tricks.
3. Boys Love (the movie).
I don't agree with the decision at the end, and I even think it could plausibly be viewed as a dream. Both young men wake in the hospital.There is a kind of fatalism about the ending, however, and I found I wasn't angry because I felt that Mamiya makes the final decision for himself with his eyes wide open. It might be the wrong decision, but he is acting more out of Lord Jim honor than any other emotion.
Not only do I think the end could be viewed as a dream, I also wrote a bit of fan-fiction in my head about the young men in heaven. In my fan-fiction heaven, people go to the heavens of their creation/mindsets. But they can change heavens. Often, they end up where they thought they would be. Sometimes, they realize, "Wow, no, this isn't where I want to be."
In addition, certain couples are automatically separated to make sure that the lives they are now living are in accordance with their moral codes and not simply what others want them to do.
The two young men here are initially separated with my detectives/interventionists--Thatcher and Damien--as go-betweens. Eventually, they are reunited.
The above examples are exceptions. 99.999999999% of the time: such endings are total cop-outs.