The reason for this is that, as all the crap about adventure and why it's a horrible thing that people must outgrow teaches us, is that Lynn seems to have an exaggerated dread of life that isn't as boring and safe as possible. This is a woman who made a hero out of a crazy idiot who's traumatized for life because her children move around when she's not looking at them and who is also overwhelmed by having to deal with cross-town traffic. Actually flying up to somewhere unfamiliar and having to go without snacks and beer for three days would be so horrible, she'd simply sit down and will herself to die to spare herself the horror.
This is why we see the irritating and obsessive need she has to leave anything interesting about her family on the cutting room floor in order to ward off the horrible feeling that she's a boring drone who fears things and misses out on life because she's too afraid of life to live it. Her real family are interesting people who do interesting things that she's too chicken to do; the family she wants aren't going to notice it at all when they drop dead of boredom.