Believe it or not, my parents' inevitable demise is a strong motivation to CTB. It sounds so trite when so many people on this forum struggled and survived through awful, abusive childhoods and terrible parents who caused their SI and who they wished were dead... But despite all their faults (I fought like cats and dogs with my mom until just a few years ago) my parents are amazing people who always took care of me and my siblings through our whole lives. Nobody will love me like they do and this relationship simply can't be replaced. Whatever shit happened in my day, it can always be made better by coming home and chatting with them. The idea of not only living through their decline/passing but having to live for possibly DECADES with the grief and pain of not seeing them again? And knowing that unlike other phobias/anxieties, this one is rooted entirely in inevitable fact and there's nothing I can do to stop it, prepare for it, or even predict when it will happen? Nah, fuck that. My friends put me on the back burner as soon as they got married or found cooler friends, no man will date or procreate with me (my dream) and my siblings will be fine after a few months. I'm not living without my parents.
I'm strongly considering CTB before either of them pass so I won't have to live through it, especially since 1) I'm THE biggest coward on the planet and 2) I love them both and waiting for them both to die means having to live with the grief of one passing until the other passes as well (unless they randomly both die together), but they deserve better than having to bury their baby girl, so I'm grudgingly trying to hold it off until they pass. Might be decades since they're both relatively young/healthy but you never know (which doesn't help my depression/anxiety that is also encouraging me to CTB), but I've had SI since I was in middle school and I've been patient this far.