Explanation of the reason the hadith scholars collected hadith in their books without distinguishing between the authentic and the defective?

The Shaykh : So that a negligent or ignorant person does not say—and we have heard this many times and again—“What is the matter with those hadith scholars who collected hadith in their books without distinguishing between the authentic and the defective, as the two Imams al-Bukhari and Muslim did?” They say this with a tone of reproach, unaware of the fact I mentioned, which is that this collection, which was the work of the great majority of hadith scholars, was a necessity. As we also mentioned, it was a preparation for distinguishing the authentic from the weak. For example, we find among the famous books currently circulating among Muslims, “Musnad Imam Ahmad ibn Hanbal” (may Allah have mercy on him), in six large volumes. However, the reality of this great book is that it contains hadith of all types: the authentic, the good in its two categories (authentic in itself and authentic due to other evidence), the good in itself, and the good due to other evidence.
The student : And the good due to other evidence.

The Shaykh : No, it contains the authentic in its two categories: authentic in itself and authentic due to other evidence. It contains the good in its two categories: good in itself and good due to other evidence. It contains the weak, which is also in its two known categories in hadith terminology: the weak that is not severely weak, which is suitable to strengthen other hadith of its kind; and the weak that is very weak, which yields nothing to the one who looks at it except to know its weakness and defectiveness. It contains some weak hadith. This book, this massive book—some people ask why Imam Ahmad did not purify this Musnad of weak and fabricated hadith. We say: It is sufficient for Imam Ahmad in terms of merit that he dedicated his entire life to collecting this Musnad from various Islamic lands. You know that Imam Ahmad is one of the four Imams of the jurists, the Muslim jurists whom the masses of the people of the Sunnah follow. Perhaps you know with me that this Imam, who is the last of the four jurist Imams, is the most knowledgeable of these Imams in hadith, and indeed more so than others, not only among the jurists but also among the hadith scholars. Why? Because he devoted his effort to collecting these hadith in this great book, thereby paving the way for purifying these hadith and distinguishing their authentic from their weak. It is no surprise that this Imam, Imam Ahmad, is among the teachers of the two Sahihs, the teachers of al-Bukhari and Muslim, for they narrated from him in the “Sahihayn,” in addition to many other hadith in other works. I said: The majority of hadith scholars’ concern was collecting hadith from the memories of the narrators at that time. Then followed another majority whose concern was writing these hadith and collecting them in books as well, in that manner of collection without investigation, collection without distinguishing between the authentic and the weak. Thus, these many books that Muslims today, scholars and students of knowledge, circulate. But among these were those who aimed for the goal of that collection and arrangement, which is distinguishing. Among these, as we said, was a group of the early ones, including Imam al-Bukhari and Imam Muslim, and a few of the later ones.