grammar - Why are "and/or" constructions in English not considered grammatically correct?

Why are "and/or" constructions in English not considered grammatically correct?
Consider, for example, the following sentences:

• "Multi-organ failure can be attributed to confusion, fatigue, and/or
  
  delirium not attributable to any other cause."


• "Multi-organ failure can be attributed to either confusion, fatigue, delirium, or all of them, not attributable to any other cause."

Also, suggest any other way to avoid/reword such constructions.