"Why do you not want me to make it?"
Translation:Pourquoi ne voulez-vous pas que je le fasse ?
Well, because by the rules of French grammar, it is triggered by vouloir que in the positive or negative.
Vouloir que just happens to be one of the phrases that trigger the subjunctive. There are many phrases which trigger the subjunctive. You cannot ignore the subjunctive and you cannot use it only some of the time, you just have to learn which phrases use it and which don’t. Lawless french provides a lesson on the subjunctive. Certain phrases which express certain desires and certain feelings trigger the subjunctive. Vouloir que is one of these phrases.
Because the construction is all wrong.
The main clause "Why do you not want ..." translates into the polite inversion : "Pourquoi ne voulez-vous pas... " although, if talking with a very close friend or family member, you could say:
"Pourquoi ne veux-tu pas.... "
Then you need to connect the subordinate or dependent clause "me to make it" which is expressed as: "que je le fasse " .
A useful subjunctive tool to can be found here: