"Following informal practices in the biomedical sciences,
the last author often gets as much credit as the first author,
because he or she is assumed to be the driving force, both
intellectually and financially, behind the research. Evaluation
committees and funding bodies often take last authorship as a
sign of successful group leadership and make this a criterion
in hiring, granting, and promotion. This practice is unofficial,
and hence not always followed, meaning that sometimes
last authors “mistakenly” benefit when they actually are
not principal investigators"
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.0050018