The differecne is that the eastern front wasn't anything near the western front. The frontlines were so much longer that it wasn't possibly to have true trenchwarfare. Troops were dug in, surely, but all the battles were mobile.

There is no doubt in the effectiveness of the tactics and results of the offensive, but it simply can't be applied to the western front.
The arty is too inaccurate (doctrine has been on rate of fire, which is a lot easier to learn btw), and the density of defenders is too great. A wide front attack would simply cause more casualties for the Allies.
Also I severely doubt the casualties. Yes the Austrian forces were bust by then... obviously. But 3:1 against the Austrians and nearly 1:1 against the Germans. That is almost 4:1 losses in favour of the Russians, way way better than any other offensive of the war and only bested by the Germans in the much smaller Lake Naroch Offensive. Even Tannenberg is nothing in comparison.

So had the Russian offensive really been that great it would have ended the war right there. Just short of 2 million fighting men lost in two months when the total manpower on the eastern front was around 3 million for the central powers, if that at all.
Such a lopsided result would have meant a breakdown of the east and the Russians coudl easily have started a new offensive since they were now very much superior in numbers.

Obviously the losses were almost crippeling for the Austrians (they never recovered), but the German forces did very well for their part and when they did well against the Russians they gave at least 1:1 losses. So either the Austrians let te Russians do about 12:1 losses on them, or else the Russian figures doesn't add up. After all they were exhausted by the offensive, and exhausted means you can't find any more men, not a physical exhaustion (people recover within a few days unless they become metally unstalbe at which point they are either shot or written off as casualties). The Russians could find many more men than half a million. A total of around a million would still make it a supremely effective offensive. Oh well... we will never know I'm sure.