Obvious questions that the Gemara doesn't ask

Many times when you learn Gemara there is an obvious question on the Gemara either in logic or a contradiction to another Gemara and the Rishonim work long and hard to answer it and come up with different contradictory answers. The question is why didn't the Gemara itself address this question.

Today's Daf (Sanhedrin 61) has a perfect example of this. The Gemara while discussing Avoda Zara brings a dispute between Abaya and Rava about someone who worships Avoda Zara out of love or fear. Abaya says he is חייב and Rava says he is פטור. The Rishonim ask an obvious question, Rava agrees later (74a) that a person must give up his life in order not to transgress the sin of worshipping Avodah Zarah. How can we reconcile this with Rava's statment here that a person is not liable for the sin of Avodah Zarah if he worships it merely out of fear of another person? Why does Rava say later that he must give up his life in order not to be coerced to serve Avodah Zarah if someone who worships out of fear is not חייב? This is such an obvious question that we need to ask why didn't the Gemara ask it. Of course the Rishonim give various contradictory answers:

1. Tosafos - Rava holds that a person must give up his life in order not to serve Avoda Zara, however, if he does serve out of coercion he is not חייב.
2. Ramban - redefines out of love or fear. He says that means that he is scared that he will suffer financial harm if he does not serve the Avodah Zarah. 
3. Ran - Rava only says that you must give up your life if you will be forced to worship the Avoda Zara and accept it verbally as your God. However, just coercion to worship does not require you to give up your life.
4. Rambam - redefines out of love or fear. "Out of love" refers to a person who worships Avodah Zarah because he feels a strong attachment to the beautifully crafted statue, and "out of fear" refers to a person who worships Avodah Zarah because he is afraid that the statue will hurt him if he does not serve it. 

We see from here that the fact that the Gemara didn't ask this very obvious question leads to tremendous confusion about how to answer the question.