Sheikh al-Sharîf Hâtim al-`Awnî
To begin with, a word is in order about the author of Sunan Ibn Mâjah. His name was Abû `Abd Allah Muhammad b. Yazîd al-Qazwînî, better known by the epithet "Ibn Mâjah". He died in the year 273 AH.
He was one of the leading scholars of the Sunnah whose reliability as a narrator was renowned. He had preserved and recorded a considerable amount of the Prophet's Sunnah. Moreover, his work Sunan Ibn Mâjah is recognized as one of the six most important books of hadîth, which is saying a lot.
The reason there are a number of weak hadîth in Sunan Ibn Mâjah is because some of narrators in the chains of transmission for those weak hadîth are narrators who are unknown or who were known to be weak narrators. The weakness of these hadîth has nothing to do with Ibn Mâjah himself.
Ibn Mâjah does not set out to record in his Sunan only hadîth with impeccable chains of transmission. His purpose is to record hadîth that are often cited as evidence for various Islamic teachings and legal rulings, and he gives the full chains of transmission that he has for those hadîth. He allows hadîth which have chains of transmission with various degrees of strength, though he does not knowingly record any hadîth that is fabricated or outright false.
Ibn Mâjah's was compiled after the other five main hadîth collections. Those earlier collections had already recorded between them the vast majority of authentic hadîth from our Prophet Muhammad's Sunnah. Therefore, it makes perfect sense that a number of the hadîth he records that were not already recorded in the previous five collections are weak, especially since Ibn Mâjah did not stipulates as a condition for his book that every hadîth recorded therein must have a strong chain of transmission.
It is true that many of the hadîth which are found only in Sunan Ibn Mâjah among the sis main books are weak or even very weak. However, this is not true for all of them. A few reach the grade of Sahîh (authentic) while others are good and acceptable. However, it remains that the majority of those hadîth are indeed weak.
You can find where some scholars have written that "Any hadîth which Ibn Mâjah is alone in recording is a weak hadîth." However, these scholars are simply generalizing, since it is true for most of those hadîth that they are weak.
And Allah knows best.
Source: Islam Today