Question Why do xianxia MCs that pursue immortality always outlive their parents?

It's a very obvious explanation .For the mc to develop in a story with one pursuit be it revenge/stolen love interest/immortality.The author would need the mc to only focus on said issue to keep the story flow stable and constant.So he would either slowly remove the baggage that would make a normal human think in after thought during their idle travel or he would make a plot to add on to his goal example being 'killed by a enemy' thus adding weight to w.e goal the mc is having.