I don't think one is necessarily weak-willed or strong-willed if they can't commit suicide. Nor do I think the opposite (that is I don't think people are weak-willed for not commiting suicide)
Imagine the following; Someone living on their own no parents, no family, no friends, surviving off the government. rotting behind PC all day.
Vs
Someone with family members that care about them, maybe they're working/school have 1 or 2 friends.
The second person has far more reasons to stay alive on the surface, even if they are suffering. But if they don't care about their families, if they personally belief their future is doomed anyway for one reason or another. If they are more selfish they might commit suicide. But that's not because they're weak willed, it's because they decided to weigh their options, concluded that there is more value in dying than staying alive.