Your point is well taken. There are now and were then better bullets than the 30 M72; however we digress. The original question was “Why breakdown and reload the LC 68 Ball?”
The LC 68 ball was free and 30 M72 bullets were available for about two cents a bullet. With a little effort; trimming the cases to a uniform length and neck sizing, weighing the bullets to a + or - 0.1 grain, and keeping the powder charge to + or – 0.1 grain one could load reasonably accurate target loads suitable for practice, DCM qualifications and local matches which rarely exceed 300 yards. The 30 M72 bullet has a better BC than does the 30 M2 and is generally more uniform and is easier on barrels (according to FA tests). Practicing with ammo of unknown accuracy is an exercise in futility.