Brother salam aleykom
You have raised two question here:
1) why there is no prophetic narrations?
2) why there are contradictions in shia narration books?
To answer the first question I have to say that you cannot tackle this issue based on the sunni beliefs and fundementals, when we have a narration from Imam Al Sadegh or Imam Al Baqer (peace be upon them) it is considered the sayings of the prophet (as). Ahlulbeyt have nothing from their own. They have inhereted this knowledge from the prophet (peace be upon him and his progeny). The prophet said: "I am the city of knowledge and Ali is the gate, whoever wants the city should enter through the gate." So these narrations from the Ahlulbeyt (peace be upon them) that you mention are all from one source, the prophet. This knowledge that Ahlulbeyt have are passed down from the prophet to Imam Ali to Imam Hassan to Imam Hussain until it gets to the Imam of our time Imam Al Mahdi (may Allah hasten his emergence). That is why we shia stress on the fact the we must receive our knowledge and teachings of Islam from Ahlulbeyt (as) because their source of knowledge is Rasulallah (as). When we say Imam Saqegh said so and so or Imam Baqer said so and so it means Rasulallah said so and so. This is our belief. Now if you don't agree with this belief and the fact that Ahlulbeyt are the inhertants of prophet's knowledge and wisdom, this is a different story to be discussed in a different topic. I hope this little answer was helpful with your first question.
Regarding the second question and the contradictions you mentioned in our narration books: I have to say that we do not have something called Sahih book. Each narration is to be studied intellectually and to be compared to the Quran, if it did not match the Quran then "it is to be hit against the wall" (as said in Arabic). Now the job of our early scholars who have collected these narrations was to collect, collect, and collect these narrations from here and their and put it in one book, regardless of them being authentic or not, ther were just collecting them. Their life time did not allow them to analize and distinguish the authentic from the unauthentic narrations because it would take ages to do so. Therefore, it was the responsibility of the scholars who came after to study these narrations and their authenticity and to extract the true teachings of Islam from these mixed narrations. Therefore the contradictions you are talking about in our narration books, if any, is normal because it is not Sahih books, they are just books that contain authentic and unauthentic narrations. Just because these narrations are in our books does not make them authentic.
I hope I was helpful.
Brother and sisters please feel free to corrected me if I had some mistakes.