That’s actually not true. One of the things we understand about suicide is that it’s often an impulse decision, and access to immediate and reliable means of suicide has a huge impact on overall suicide rates. Even moderate barriers to suicide can actually permanently reduce the rate of suicide in a population. It’s been repeatedly shown that when one method of suicide is made harder, the decrease in that method are not completely offset by other methods.
So when we do seemingly minor things like eliminating CO in domestic gas (“head in oven” was a common suicide method due to CO), increasing the height of railings on a bridge, or even making someone purchasing their first firearm wait a few days, this can often have a significant impact on whether someone actually ends up killing themselves. Suicide isn’t at all inevitable like you say.
What you and professionals consider an "impulsive decision," many depressive types have been considering or have considered but never told anybody for a long time. It only seems impulsive to you because it appears to be random. If anybody has any understanding of human psyche when they're depressed, they would know it's something you plan but play pretend to others so they don't suspect you need to be "locked up for your own good," as what tends to happen to people who try to seek help.
Mental health problems don't persist simply because people can easily buy guns and kill themselves. They continue because people are afraid their going to have their liberties taken away simply because they want help.
So when we do seemingly minor things like eliminating CO in domestic gas (“head in oven” was a common suicide method due to CO), increasing the height of railings on a bridge, or even making someone purchasing their first firearm wait a few days, this can often have a significant impact on whether someone actually ends up killing themselves. Suicide isn’t at all inevitable like you say.