I think I get it now. Your comment is both helpful and confusing because it's right and wrong. There are times where German doesn't use the plural like in English, but there is also a lot of times it does (like in this case).
It would be hard to explain without an example but basically something can have multiple of something else within that one thing, or multiple throughout many things. This would be the second case and within that case you always write the plural form.