Among the greatest sages of Israel were wood-hewers and
water-bearers; some were blind; nevertheless they involved
themselves in TT during the day and at night; and this group
includes the bearers of the tradition all the way back to Moshe
Rabbenu (Moses our Teacher).
Q1: This entire Halakha seems superfluous; we alrady know that
every man is obligated.
YE: Perhaps this is a continuation of the previous Halakha and is
both exhortation and modeling for anyone who wants to claim that
they are too busy. Also, see the Gemara in Yoma (35b) of how
Hillel destroyed any poor person's defense for not learning.
Q2: Why add that some of these manual laborers and blind men
were bearers of the tradition?
YE: This is the exhortative part - that not only are we all
obligated in study, but noone can claim that there is no value to
learning since he won't achieve greatness due to his poverty/work