The idea of death- and the assumption that it could be an end to pain- is way more enticing than the reality, because death is inherently unpleasant and not without suffering in most cases. After being suicidal over half my life at this point, I realised that fantasizing about the end is comforting, as it doesn't require me to commit to the decision to die in this very moment, it's more a self-assuaging reassurance that someday this suffering will end whether I finish things myself or let nature take it's course.
Acually going through with it and having to consciously perform the actions to end myself is a different story entirely. Even when life is inextricably painful and difficult, there is something final and unknown about death that activates the biological instinct of self preservation, no matter how hard the mind fights to be free of such a limitation.
There's a song I heard recently that has the lyrics, "Maybe death is like falling asleep." It's easy to build up preconceptions and ideas about what the afterlife- or lack thereof- would entail in our minds, and to find refuge in those things. But the dying process itself is messy, often undignified, and at odds with the peacefulness a suicidal person often yearns for. This juxtaposition I think makes everything so hard and complicated. If I could snap my fingers and stop existing tomorrow, I'd do it, but going through the long, drawn out process of suicide is terrifying.
You shouldn't have to be living in your car and dealing with the constant discomfort of such a situation, it's a real shame that you've been put in this position and not been given any help to lift you out of homelessness.