Time to blow your mind.
The longest recorded killshot in history was a mile and a half shot from a jury rigged .50 cal machine gun. In Vietnam.
Only because "recorded killshots" have to be verified, and when you are shooting 2 miles into enemy territory, there is no one to verify that the guy is dead. Your information is out of date as well, there are 3 shots since then that top the one made by Carlos Hathcock with a Browning MG.
There's also the issue that modern wars have mostly happened in urban areas, so shots over a half a mile just aren't attempted. Yours is a very misleading statistic, even if it was true, and does not actually show that snipers are less accurate now than in ww2.
The cheytac intervention is the most accurate rifle I know of, able to shoot 19 inch groups at 2100 yards. In WW2, firing at ranges longer than 1500 yards had a large degree of luck.