I think it is so rarely discussed in history because it is so large and diverse in its effects as to be incomprehensible. The ancient pandemics, save perhaps the Black Death, are similarly mostly ignored, so I don't think that is limited to only the Spanish Flu.
As to a possible divergence - in September 1918, Lloyd George contracted the Spanish Flu and was gravely ill for some days. If he had died, not only does his successor greatly influence the tragectory of Britain during the 20s, but removing Lloyd George likely leads to a British delegation more friendly to the French.
For some other famous people who could have died from the flu, here is a
fun little list.
fasquardon