1Chr 4:31

“these were their cities until David reigned The meaning is that when [the population of] the children of Judah grew, they complained about the children of Simeon in the days of Saul and wanted to drive them out of their land, but they could not drive them out, especially since all his [Saul’s] days were occupied with trouble and wars; but when David reigned, his tribe came to request from the children of Simeon the land that they had lent them, and David went and drove them out, for Saul had not been concerned with this matter because of [his] hatred for David, who was from Judah. This is the meaning of what is written: “... these were their cities until David reigned,” but when he reigned, he drove them out. [I heard this] from Rabbi Eliezer the son of Meshullam of blessed memory, and so did Rabbi Solomon the son of Levi, the brother of Rabbi Moshe Hadarshan explain it.”

“These were their cities unto the reign of David - It appears that David took some of the cities of the Simeonites, and added them to Judah; Ziklag for instance, Sa1 27:6. As the tribe of Simeon had withdrawn their allegiance from the house of David, the kings of Judah extended their domination as far as possible into the territories of that tribe, so that they were obliged to seek pasture for their flocks at Gedor, and in the mountains of Seir, as we find Ch1 4:39-42.”

“David, who had Siceleg given to him, 1 Kings xxvii. 6. (Haydock) — After the schism, Juda straitened the tribe of Simeon; so that it was forced to seek for other habitations in Gador, under Ezechias, ver. 39., &c. (Calmet) — It could no longer reside among those of the tribe of Juda, (Du Hamel) and acknowledge another king. (Haydock)”

“These were their cities unto the reign of David--In consequence of the sloth or cowardice of the Simeonites, some of the cities within their allotted territory were only nominally theirs. They were never taken from the Philistines until David's time, when, the Simeonites having forfeited all claim to them, he assigned them to his own tribe of Judah (Sa1 27:6).”