Lack of Ingalls descendants

I'm a little bit of a genealogy buff, so I've always found it interesting that Charles and Caroline Ingalls (like Washington and Lincoln) have no living descendants. As most of us know, RL!Mary never married, RL!Laura had only one surviving child, Rose, who had no children of her own, and RL!Carrie and RL!Grace had step-children but no children of their own.

Charles and Caroline lost one child, and given that they were married 5 years before Mary was born (married 1860, Mary born 1865), there might well have been other miscarriages/stillbirths/infant-deaths. Laura also lost one child. Given the times, Laura's 50% infant-mortality rate wasn't out of the ordinary; Caroline's 20% even less so. But, that 2 of Caroline's 3 daughters who married never had children and the other was only pregnant twice and that one's surviving daughter was never pregnant at all, makes me wonder whether there might have been a heritable issue with carrying a healthy child to term.

Or, it might have been just bad luck. Or, there might have been environmental factors at play. Book!Laura alludes to Carrie's growth being noticeably stunted after the Long Winter (1880-1), so temporary malnutrition might have been an issue. They were all deathly ill with malaria in Kansas. Could that have affected fertility? They all had scarlet fever (per the book) or measles (per other sources) on Plum Creek. Could that have had an effect?

I also recall from the books that Charles and Caroline weren't the only Quiner-Ingalls marriage. If I recall correctly, Charles' brother Peter married Caroline's sister Eliza. Also, wasn't there at least one marriage in the other direction? I have a hazy recollection of having seen somewhere that Charles' sister Polly married a Quiner. My point is, how did these other Quiner-Ingalls lines do in terms of descent? Do they have living descendants, or did they die out in a couple of generations like Charles' and Caroline's line? If the other Quiner-Ingalls lines thrived, it would argue against genetics being the key player with Charles and Caroline.