Because the articles have to be concise to be readable? For example I just stumbled into the article "Tinnitus" (http://en.wikipedia.org/wiki/Tinnitus) which contains a "list of notable individuals with tinnitus" (given that tinnitus is common, this is analogous to a list people who like the colour beige). Makes the (medical) article a bit longer, but crucially it fills the references sections with totally irrelevant links.
What would argue against making it its own article? Instead of deleting, these parts can just be separated- and storage is only getting more plentiful by the year.
