I recommend you see these videos then let me know if you have any follow up questions:
In brief, we don’t follow a marja. We follow the Imams. We just refer to marjas because they are experts. Also, our mainstream marja’s don’t reject hadiths. If it appears to you that they are, it might be one of the following cases:
1- They don’t consider the hadith authentic based on their research
2- There is a conflicting hadith that makes them not issue a fatwa based on the first one
3- They believe it was issued in a specific context that may not be applicable today.