Sometimes I think it's more of what the others want than us. I hear way too many times that suicidal people are "selfish", yet I see so many times how we are thinking about our loved ones, our pets, who will take care of them, what days to not do it on so they don't have bad memories on special days, what method to use sometimes to make it easier on them, even how to delay call an emergency service, or using a hotel, just so family doesn't find us, but a stranger does, or a person trained for it. That's selfish? Our last acts are thinking of others practically.
And then like others said, they can't imagine being in pain of one type or another all the time, or think that they'd want to live no matter what, even though the worst thing that probably happened to them was a broken bone or toothache.
But I kind of view it too like with my grandmother. She had a DNR. When she was in the hospital on her last days, they had her intubated to keep lungs inflated so she could breathe. Everyone thought I was sad because she was dieing, but I said "she doesn't want this". They asked what I'd do and I said "pull it", and my mom and her husband (who put her there--jerk), was like "OMG HOW DARE YOU!" what if she was your mom! wouldn't you miss her? But I was like She's my grandma, I love her, I don't want her to die, I want her around, but this isn't what she wants. And even then, they still couldn't get past the it wasn't what they wanted, it was what she wanted--even though she had it in writing.
So I think people's reaction to suicide is like that. They don't want the person gone, and they don't care what the other person wants, it's all about them and their wishes (the person not wanting to die). So they try to stop them, prevent it, constantly try to revive them if they can. Because their thought is, and I've heard it before with attempted suicides, "how could you do this to me". Never thinking that maybe the person just wants to die, and it has nothing to do with them.