I'm thinking that if a fish actually visibly falls ill and dies, then something is definitely wrong and the potential fishkeeper can learn the lesson about causes and remedies.
If a fish survives, then that lesson may not be learnt, other than the fact that I don't have to learn proper fish care, because my fish will survive anything!
In such cases, when the fish then dies earlier than it should've, the cause may then be identified, (wrongly), as 'old age' or a more obvious disease, such as ich. The fact that the fish died because it wasn't living in ideal conditions for a long time, was stressed and more prone to stresses/diseases, would be missed.