Probably from some sort of illness (not necessarily bacterial or viral). Cancer does get a little more than 1 in 3 people in their lifetimes. Further, although lifestyle (socioeconomic status) does contribute significantly to whether someone does get these more common illnesses (heart diseases, cancer, alzheimer's/dementia), genetics also contributes as well.
I'd like to think I would die because of old age but as things are it's probably my unhealthy lifestyle, early morning sleep or be unknowingly infected by the corona virus or an even worse pandemic virus.