"Why do you not have a dentist?"
Translation:Warum hast du keinen Zahnarzt?
Zahnarzt has a dual use : gender specific (male), and non gender specific. Zahnärztin is only gender specific. "Warum hast du keinen Zahnarzt" is, primarily, a non gender specific question : why don't you have any dentist at all? "Warum hast du keine Zahnärztin" is a different question : why don't you have a female dentist (instead of a male one). German, and other European languages, contain many gender specific nouns, whereas English is getting rid of them, and also moving towards non gender specific pronouns as well. Arguably, it is the existence of feminine markers in German nouns that cause the problem. If you don't like the way German works, however, don't blame DL.