Humans are programmed to live and survive, it is how we have evolved. Even know we want to die, it goes against our instinct to survive. Of course ctb is very difficult. Methods can also fail. I believe, that at least in my case, I will have to reach a point of desperation in order to leave this world.
There really is so much suffering in this world and there is no limit as to how bad things can get. If we think we have it bad now, it can get so much worse. There really should be the option of euthanasia, it is cruel how the society expects us to suffer for decades. In general, I think humans are programmed to live and to try to find solutions to their problems. For many suicide is an ultimate last resort and they will only do it when things are completely hopeless, so that could be another explanation as to why more people do not ctb.