Why isn't Muwatta of Malik as famous as the six books of hadith?

Question

I am confused that the Muwatta was not included in the six books of hadith, considering that it was made earlier than all of the six books, so it should be even more reliable then the six books.

Answer 1

The six hadith collections

Your claim is not 100% correct the six hadith collections are:

1. Sahih Bukhari, which was collected by Imam Bukhari.
2. Sahih Muslim, which was collected by Imam Muslim.
3. Sunan an-Nasa-i (more exactly as-Sunan a-Sughra) which was collected by imam an-Nasa-i.
4. Sunan abi Dawod which was collected by imam abu Dawod.
5. Sunan a-Tirmidhi or Jami' a-Tirmidhi, which was collected by imam a-Tirmidhi.
6. Sunan ibn Majah, which was collected by imam ibn Majah.

This is the majority view!
However there's a dispute about the 6th book some scholars considered al-Muwatta' the 6th in this collection among them are as-Saraqusti in his book called a-Tajreed fi al-Jami'i bayna as-Sihah التجريد في الجمع بين الصحاح and the eldest brother of the famous historian and mohhadith and author of al-Kamil fi at-Tareekh: Majd ad-Din ibn al-Athir (the three brothers were all mohadiths and historians however 'Ali 'Izz a-Din was the most famous among them).
Further in the maghreb al-Muwatta' was even regarded as of higher rank than the two sahihs.

So basically al-Muwatta' would be one of the 7 most authentic collections.

Note that beside the term "the 6 hadith collections" there's also the term the "nine hadith collections" which includes:

7. Al-Muwatta' of imam Malik.
8. Al-Musnad of imam Ahmad.
9. As-Sunan of imam a-Darimi

All three authors predated imam al-Bukhari or at least were born and died before him. Nevertheless imam al-Bukhari had already shown his Sahih for example to imam Ahmad before Ahmad completed his Musnad. The same could also be the case for imam a-Darimi who was born 181 a.H. and died a year earlier than imam al-Bukhari.

See also:
Original Copies of Muhammad al-Bukhari's Books?
what is the Chain of Sahih Bukhari from Imam Bukhari to us?
Which are the Sahih hadith books?

Reasons why al-Muwatta' was not counted as one of these six instead of Sunan ibn Majah

There are several good reasons why one wouldn't count al-Muwatta' as one of these six books, here the major two:

• The hadith content of al-Muwatta' is included in any later hadith collection to a huge amount (redundancy).
• The Sunan of ibn Majah has a higher amount of deviation to the content of the other five books than al-Muwatta'.

The contemporary scholar ibn Amin made a comparison between some hadith collections content compared to the two Sahihs based on an application of a company called Harf, which includes -as far as I understand- a database of hadith collections with which one could perform search and stastical analysis activities. Here's just a translation of what he shared on his website in an article about the amount of Sahih narrations -see here-:

In this article he also said that ibn Majah had compared to the other 5 books an addition of 600 ahadith at least 500 of them are da'if. While al-Muwatta' only had 50 more ahadith that were not mentioned in any of the other five.

So basically the smallest hadith collection (al-Muwatta') is the most authentic one.

Al-Muwatta' is among the most commented hadith collections

Due to the fact that al-Muwatta' is a guide line for the maliki school of fiqh and a source for other schools of fiqh among ahl al-Hadith and the version of imam Muhammad ibn al-Hassan a-Shaybani is a source of the hadith of abu Hanifa and also a source for comparison between the hadith of al-Hijaz (ahl al-Hadith) and al-Kufa (ahl ar-Ra'y) it is the most commented hadith collection and may have even more commentaries than both sahihs.

Al-Qadi 'Iyyad said in his Tarteeb al-Madarik ترتيب المدارك وتقريب المسالك:

لم يعتن بكتاب من كتب الحديث والعلم اعتناء الناس بالموطأ فإن الموافق والمخالف اجتمع على تقديره وتفضيله وروايته وتقديم حديثه وتصحيحه.
لم يعتن بكتاب من كتب الحديث والعلم اعتناء الناس بالموطأ فإن الموافق والمخالف اجتمع على تقديره وتفضيله وروايته وتقديم حديثه وتصحيحه
People did not take care of a book from the books of hadith and science as people take care of al-Muwatta', for the agreeing ^{(supporter in view)} and the disagreeing ^{(opponent in view)} gathered in appreciating it, preferring it, narrating it, presenting its hadith and correcting it.

having said that, here just a few of the known commentaries on the book:

• Ibn 'abd al-Barr compiled al-Istidhkaar الاستذكار, at-Tamheed التمهيد (which was highly praised by ibn Hazm a big opponent of the maliki school of fiqh) and Tajreed at-Tamheed.
• Al-Baaji compiled al-Muntaqa المنتقى. As-Suyuti counted two other books al-Eemaa' الإيماء and al-Istyfaa' الاستيفاء and explained that al-Muntaqa is a summary of al-Istyfaa' and al-Eemaa' is a summary of al-Muntaqa.
• Abu Bakr ibn al-'Arabi compiled al-Qabas القبس.
• Muhammad ibn 'abd al-Baqi az-Zurqani compiled a medium size commentary.
• As-Suyuti compiled a short commentary called Tanweer al-Hawalik تنوير الحوالك and Kashf al-Mughatta كشف المغطي.
• Al-Lucknawi compiled at-Ta'aleeq al-Mumajjad التعليق الممجد.
• Waly Allah a-Dahlawi compiled al-Mussawa المسوى and al-Mussaffa المصفى (in Farsi).
• Al-Kandahlawi compiled Awjaz al-Masalik ila Muwatta' Malik أوجز المسالك.
• Tahir ibn 'Ashur compiled Kashf al-Mughata ... كشف المغطى من المعاني و الألفاظ الواقعة في الموطأ .
• Mulla 'Ai al-Qari who compiled a commentary on al-Muwatta'a based on the narration of Muhammad ibn al-Hassan a-Shaybani.

See also:
Is there an equivalent to "tafsir", but for hadith?