Another rational, simple explanation is that one part of what makes covid dangerous is that is picks off those who were struggling with other illnesses but would have likely survived without the added factor of COVID-19.
I don't know that we have the data to say what the actual situation is, but it seems logical to say that some of these additional illnesses were complications of COVID, while others were pre-existing conditions exacerbated by COVID.
Either way, the idea that COVID isn't dangerous because only 6% of COVID deaths were from COVID only is bogus. I think the positive news out of this is that maybe one way to help make things better is to try to treat or prevent those other conditions. One of the reasons people believe Japan has done relatively well is widespread vaccination against pneumonia, reducing damage from COVID induced pneumonia. I'm not sure if this was proven one way or another, but is an interesting idea.