Translation:Women are as smart as men.
This sentence was probably meant as a generic statement. Not some specific men and women, but in general. In English that means the no article should be used (if it was about some specific men and women, then the definite article would be used), but in Romanian the definite article is used either way. Even so, given such a sentence with no context, it would be natural to treat it as a generic statement.
The same purpose as not using the definite article in English.
That's how you generalize over a concept in Romanian. I'm not sure how it would sound without definite article but in Hungarian it would sound like "some random women not even worth referring to, are as smart as some random men".
"women in general" is a very definite concept to me hence I use definite article. Romanian might be similar in this regard.