Suicide is something that just claims a lot of lives. The tragic thing is that often these people are not beyond help and just get caught up in a desperate moment. So, I can see the value of a phone number that is there. Of course suggesting that as a solution to somebody that is suicidal is not always going to produce the desired outcome. But it's not like that that is going to push them over the edge either. And I imagine there are people that do call and live. The math is probably in favor of that number being there for those who need it.
Of course some people really are determined to end their lives but for many this is just a desperate way to solve a seemingly desperate situation that objectively isn't actually that desperate. People with mental health issues often have trouble doing rational things and sometimes just calming them down gets them to a stage where they are at least open to being helped. That's hard work but it saves lives. Usually that help comes initially in the form of extremely heavy sedatives. That doesn't solve any of the underlying issues but it does get them in a state where they are at least able to be somewhat rational again.
I have some relatives and friends with mental health issues that went through such a thing. I also remember talking to them while they were in the middle of that. It's just horrible to witness somebody going through such a thing and realize that they are scared of what they might do to themselves and that there is literally nothing you can say or do that changes that. I'm glad they are still there and managed to find a way past that and back to leading a happy life. But of course not everybody is lucky enough to hear what they need to hear or get the care they need when they need it most.
A common pattern with people that are difficult to help is that they reject the whole notion that they need it to begin with. Telling such people that they need help is not an easy message and it can easily result in people getting upset and angry. But not telling them is not an option either. A phone number is not a solution to anyone's problems. But somebody will answer that call regardless and it might save a life once in a while. The absolute worst case is that it doesn't, which I'm sure happens as well.