I guess it goes back to how we use categories. For me, one old-school approach I've often used in other wikis is to follow the tree from higher to lower categories, and sometimes the reverse, in order to find something (and occasionally discover other things). Coming to Category:Categories on WikiTree, I had expected to find some top-level category for something so fundamental to the lives of people recorded in genealogy as death (for those ways of dying that merited the attention of specific categories).
Re the deleted Category:Causes of Death, I don't recall accessing it for any of the work I've done, and since it's not indexed on Archive.org, I don't know what it looked like. And I wasn't part of the discussion about its deletion. I'm imagining that one problem with that category may have been with its name, which because it echoed what is generally on death certificates, perhaps invited specific subcategories that belonged further down the tree (such as under Accidental Deaths)...?
In any event, what I'm proposing with Category:Mortality would include some high-level categories that wouldn't really fit under Category:Health (i.e., Capital punishment, Genocide, Killed in Action, Murder Victims).
I'll leave it there for now, pending other possible comments from others.