An Hadith is referred to as da'if because

An Hadith is referred to as da'if because it has defects in its isnad and matn. The isnad refers to the chain of transmitters, while the matn refers to the content of the Hadith. These defects can include missing or unreliable transmitters, contradictions within the chain of transmitters, or inconsistencies in the content of the Hadith. It is important to note that a da'if Hadith is not always completely unreliable. Sometimes, it may still have some supporting evidence or it may be partially reliable. However, because of the presence of these defects, scholars consider da'if Hadiths to be less reliable compared to other categories of Hadiths. It is always recommended to rely on Hadiths that are classified as sahih or hasan as they are considered to be more authentic and reliable. On the other hand, a fabricated tradition is a completely false Hadith which has been intentionally invented and has no basis in the teachings of Prophet Muhammad (peace be upon him). These fabricated Hadiths are not considered reliable at all and should be avoided. In summary, a da'if Hadith is referred to as such because it has defects in its chain of transmitters and its content. While it may still have some supporting evidence, it is considered to be less reliable compared to sahih or hasan Hadiths. Fabricated traditions, on the other hand, are completely false and should not be relied upon.