My initial response was to just post 'skill issue' but I gave it some thought.
You're not exactly correct. Some impulsive people do end up dying on the first attempt. But many attempts are cries for help, and the methods chosen are not as effective as they could be, and the conditions are not right. The impulsivity hinders their ability to carry out the deed efficiently. The people with the highest success rates are actually the ones that plan extensively.
I just read a post from another user about their failed attempts. They seemed to plan well, but their suicide plans involved notifying friends, family, and emergency services with time delayed messages, such that the 'body could be found appropriately' which imo was counterproductive to actually dying. You don't want to be found or tell anyone, so that if it fails, you can try again or use your redundant method. So it's important that the plans are logical.
And well, accidents happen all the time, and people do die from 'internet trends' it's just how it works.