A VOA tutorial says
In English, only certain kinds of words come before nouns. Often, the word that comes before a noun is an adjective.
There are some different types of words would come before nouns, e.g. to be, verbs, prepositions, adjectives, etc, which could be "certain kinds of words" that tutorial mentioned.
Therefor that tutorial uses "kinds of". In this kind of situation, it has to use "kinds of" rather than "kind of", as there are many kinds.
Is my understanding right?
In phrase "kind of" mainly has 2 meanings, "category" and "to some extent", please have this post focus the former meaning.