Why is Al-Zuhri considered a weak narrator, and why are there narrations by him in Sahih Al-Bukhari despite his weakness?

Al-Zuhri, whose full name is Abu Bakr Muhammad ibn Muslim ibn Ubayd Allah ibn Shihab, was one of the trustworthy imams among the Tabi'in (the generation after the Companions). He was characterized by his piety, strong memory, and intense eagerness for knowledge. Prominent imams of Fiqh (jurisprudence) and Hadith (definition), such as Malik and Al-Layth, learned from him. The imams of Hadith, Al-Jarh wa Al-Ta'dil (discrediting and accrediting narrators), unanimously affirmed his trustworthiness and accepted his narrations as evidence. Ibn Sa'd described him as trustworthy, having abundant Hadith and knowledge. Ibn Hibban described him as one of the most حافظ (memorizers) of his time and one of the best in presenting the texts of narrations. Al-Dhahabi described him as the most knowledgeable among the حافظ (memorizers).