Reasons for scattering Talmudic subjects over different Masechtot

Question

It is easy to criticize the Rabbinical sources for inconsistency, as I did many times, but I would truly like to find a plausible and reasonable explanation for a certain trend in the Talmud based on my current learning.

Masechet Succah is dedicated to the Mitzvah of sitting in Succah (and 4 Minim). One would expect the subject to be covered from all possible angles. However, a very important Braytah and a whole discussion around it is brought in Masechet Erchin (3b) instead:

.הכל חייבין בסוכה: כהנים לוים וישראלים
A Baraita teaches: Everyone is obligated in the mitzva of Succah, including priests, Levites, and Israelites.

This passage discusses the obligation of Cohanim and Leviim in sitting in Succah (there's no such discussion in Masechet Succah). I understand completely, that the Baraitah is a part of a series of statements starting with "Everybody/Everything..." but that alone seems to be a bad reason to group Halachic topics if one wants to understand the Halachah as opposed to merely memorizing it. (This method of arranging discussion By-The-Way is worth a question on its own).

The Beraytah was clearly known to the editors of the Talmud, and nevertheless, they decided to put it in Erchin and not Succah (there's also a viable option of copying the passage several times).

Please help me to find a reasonable explanation of how the placement of this Beraytah in Erchin instead of Succah helps to understand the topic of sitting in Succah?

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Please:

• Do not comment "that's the way they did it back then" as we hold the Talmud eternal.

• Do not comment "there are tens of other examples" as it does not help in the understanding of the phenomenon

• Do not comment "the purpose of learning Torah is to merely engage in reading/murmuring Talmudic passages", as this question exclusively addresses the goal of understanding the Halachah

• Do not comment "it proves one should be proficient in the whole Sha"S" as it is just a huge drawback caused by a decision to scatter the subjects over the Talmud

Thank you.

Answer 1

The Midrash (Kohellet Rabbah Parshah 1) states the following:

לטובתו אדם למד תורה ושוכח שאילו היה אדם למד תורה ולא שכחה היה מתעסק בתורה שתים שלש שנים וחוזר ומתעסק במלאכתו ולא היה משגיח בה לעולם כל ימיו אלא מתוך שאדם למד תורה ושוכחה אינו מזיז ואינו מזיע את עצמו מדברי תורה

It is for his benefit that man learns Torah and forgets. For if man would learn Torah and not forget, he would engage in Torah for two [or] three years and then return to engage in his work, and he wouldn't concern himself with it [Torah] for the rest of his life. But now that man learns Torah and forgets, he will not abandon or depart from the words of Torah.

One could perhaps similarly argue that if each topic was precisely confined to its own tractate, people might decide to only learn the topic that interests them the most. Someone might decide that he wants to become an expert in Succah and might therefore only learn Masechet Succah. This would cause large parts of Torah to be abandoned.

By spreading out the topic over various tractates, even someone who only wants to learn about Succah will be forced to learn other things as well in order to cover all the Succah content.