> but not to some event in 2017 that resulted in extra deaths vs. any surrounding years

But that's exactly what the paper shows. It's reasonable to ask the question why was the difference in deaths far greater in 2017 than in the surrounding years and why was the mean age of the persons excessively dying so relatively young? There most likely are structural differences causing excess US deaths, but the claim that those structural differences caused a huge relative spike in one year for no particular reason isn't very satisfying.