Jamieson, Fausset and Brown on 1 Chronicles 4:31-43

31-43. 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 (1Sa 27:6).