They list how people died in the paper, and point to an increased risk of fractures on some drugs, and gastrointestinal bleeds in others. All-cause mortality can be a helpful metric for a drug, because it looks at the overall positive and negative effects on the death rate as a whole, to see what the balance is. Additionally, all-cause mortality over a large cohort means not being blinkered by the ways a drug might be ‘expected’ to cause or reduce death. Analysing all causes of mortality is useful in this way, and can give meaningful indicators about whether a drug is worth taking, taken into context with things like quality of life improvements.
Additionally, this is one study. I feel like this always happens when a study is posted to Reddit; people always act it’s trying to tell them what to do, and that is not the case usually. This is one piece of evidence in a broader body about the risks and benefits of antidepressants.