Jim's points, made earlier, on the reasons for the banning of "expanding" bulletts in warfare are accurate and deserve a reread. There was widespread opposition to England's colonial wars in the late 1800s. One section of those who opposed British conduct in India argued for a more humane imperialism by banning certain weapons of war. Like Princess Diana's opposition to land mines a decade back, they could duck the question of opposing a war by arguing for more "humane" weapons...
The Hague agreement was in response to the use by the British of expanding ("dumdum") bullets in India and what is now Pakistan. As noted, the real reason was not to be "humane" but to embarass the British over their colonial policies.
But such thing could not have come to pass before c. 1900. The real reason for going to jacketed bullets was that with the new high velocity ammunition in small bore rifles, bullets had to be jacketed to prevent them stripping in the rifling and being wildly inaccurate. So the major powers were simply making a pretense of humanity out of what was really a technological necessity.
But as Jim pointed out by the time the conventions were signed it was a moot point. Ball ammo has been used for 100 years now (since the Germans developed the Spitzer bullet for the Mauser) by militaries around the globe for several reasons...
It feeds more reliably under rough conditions and is less subject to deformation than HP. It tends to be ballistically superior.
It is cheaper to produce.
Armies are not usually concerned with "overpenetration". In fact penetration is preferred.
The hit to miss ratio in modern combat means that the cost effectiveness of hp ammo would be unviable and unnecessary. It would be a complete waste of money. So much so that the proposal would be laughed at.
In a combat zone wounded soldiers require more care than dead ones and are more detrimental to morale.
The U.S. is one of only a few nations that still use cluster bombs. White phosphorus and "Daisy Cutters" are part of the arsenal as well as chemical weapons. If there was a role for hp ammo for regular troops it would be issued. But there is no need for it and it would not be useful from the point of view of arming an army.
In other words, the U.S. uses ball ammo not for "humanitarian" reasons but because it best meets their needs. If anything hp ammo is more humane.
tipoc