What is the wisdom behind the inheritance of the deceased's brothers along with his daughters in the absence of a male child for the deceased, and their not inheriting in the presence of a male child?

All brothers are excluded by the son, so they inherit nothing in his presence. This is based on the rule of exclusion in inheritance, which states that collateral relatives do not inherit alongside a male lineal descendant. This has been established by both textual evidence and scholarly consensus (Ijma'). From the textual evidence is the Hadith: "Give the prescribed shares to those entitled to them; then, whatever remains is for the nearest male." The word "nearest" (الأولى) means the closest, and the son is closer to the deceased than his brothers. As for consensus, Ibn al-Mundhir narrated the unanimous agreement of scholars that brothers are excluded by the son, even if he is a grandson (i.e., of a lower degree).