It is easier for people to make a social media post or slap a sticker on a car than work towards some sort of meaningful social or cultural change that would benefit the wellbeing of suicidal people.
Not to say that the low effort actions aren't in good faith, I think many people do believe they are raising awareness for a charitable cause when they promote these sort of slogans and brandish the relevant merchandise. Some people may have a personal connection with suicide and so these trinkets probably have a lot more meaning and sentimentality to them than a random middle age Facebook user whose just shared a "fuck suicide!!" graphic because their friend/family member posted it.
However, many times the money raised by donations/sales of these products goes to harmful organisations which promote locking suicidal people away in psych wards, or these campaigns posture the idea that every single suicidal person has a temporary mental illness and is thinking irrationally, which is probably the biggest harm here.