It'd be a stretch to say the Russians still had more men after the Battle of Austerlitz. In the course of the battle, the Allied army lost roughly 36,000 men of their 82,000, for a total of 46,000 against the ~70,000 the French had after the battle. There were many troops not present at the battle on both sides, but it'd be difficult if not impossible to use many to make up the balance.

However, numbers don't tell the whole story. The most obvious reason the Russians didn't attack Napoleon again is because the Austrian emperor approached Napoleon to sue for peace the day after the battle; after a short meeting, the two agreed to an armistice. Carrying on a war in central Europe against France without a major ally was plainly beyond Russia's capabilities. While the Russians already intended on a total withdrawal, Austria's necessity of making peace without them ensured they could not reenter the lists until they had gained a new ally in Central Europe.

Moreover, focusing too much on numbers obscures other factors that determine how an army performs in battle. In general, battles raise the spirits of the victors, but they depress those of the losers to an even greater extent. Much of the Allied army had dissolved in panic on the battlefield; tens of thousands were taken prisoner and almost two hundred guns fell into French hands, two of the classic signs of collapse. As the Allies retreated, their columns hemorrhaged broken vehicles and baggage, confirming the breakdown of order in the army.

In terms of morale, attempting to fight a second battle after a defeat is generally quite foolhardy. Before Austerlitz, the Allies could have believed that their superior numbers, their discipline, and the talent of their commanders would allow them to beat the French. Austerlitz revealed all of these factors to be insufficient; among the retreating Russians and Austrians, there could be no doubt that their enemy not only was stronger before the battle, but that this superiority was magnified by the extent of the victory. The material losses and moral deflation reacted upon each other. Without hope of victory, the common soldier could hardly be expected to fight well, and a second battle would likely have led to annihilation.