Hero of the simple

I have a question about Rashi's commentary on the Chumash.

Rashi said that the purpose of his commentary is to explain the simple meaning of the text. Yet there are many times in his commentary on the Chumash where he provides a detailed analysis of grammar and etymology of words.

My question is how is this keeping in line with just explaining the simple meaning of the text?

I ask this question because I sincerely do not know the answer. I am not asking it to denigrate the greatness of Rashi.