I think the level of guilt one feels really depends on the relationship they have with their parents and family members. Many people here do have relatives who love them and care about them no matter what, and I imagine leaving those people behind or thinking about the impact of ctb on them is really challenging and heart shattering. Especially if that familial love and support has always been unwavering and unconditional.
For people like myself who don't really have any family members (or the surviving ones are abusive/don't care about us) it is probably harder to put ourselves in their shoes. Having loving parents is a foreign concept to me, because my father was an alcoholic who died early in my childhood, and my mother felt no love for me when I was born and didn't want me once I was a living human being rather than a romanticised concept.
When I die no one is really going to care. I don't have any close family members to mourn for me, only a grandmother who is approaching the end of her life as well due to extremely old age. My parents really should not have reproduced, as they really had no concern for the person they had created. So of course I will not really relate to those people whose parents would be devastated if they were gone, because I've never had those loving familial bonds, and I never will. However, I can understand where they're coming from.
If someone does have those connections with other people, it is understandable that they'd be concerned about those who would be left behind in the wake of their passing. Unfortunately there really isn't a good way to come to grips with these feelings or process them, because suicide is still defacto illegal in pretty much every country and the vast majority of people are not going to accept that a loved one would make this decision for themselves.
We don't really live in a world where people can have honest and frank discussions with their family members and friends about suicidality. Most people think it's a temporary affliction that can always be cured, and because of this mindset, they are going to be in denial if someone isn't getting better, even if the decline persists over months and years.
Bereaved family members tend to experience a unique sort of grief when it comes to suicide, because they think it is a preventable death and that something could have been done to help/fix the deceased, or they might harbor some sort of guilt and believe they played a role in the suicide.
I think that is why suicidal people with close family connections feel guilty, because we do not live in a culture where they could actually openly discuss their suicide with their loved ones, it will usually come as a nasty and devastating shock those left behind. There is no option to process grief with them beforehand, or come to any sort of understanding about the situation, which is tragic for all parties involved.