This is a really good point. There are a lot of really odd outcomes these mice models consistently produce but we don't know what causes them and/or don't care because it's not within the scope of the primary research question
Here is our group’s latest paper in Science. We try to get at genetics of sex differences in lifespan:
https://pubmed.ncbi.nlm.nih.gov/36173858/
In this study we mapped 7 chromosomal regions that modulate lifespan in mice. We are now up to about 35 regions. Of course the goal is to understand the actual processes modulated by each so-called “locus”.