Sure they had good cavalry at their disposal, but not enough. Seriously, if the Romans really did have enough cavalry then they would have done a lot better in wars. In Sicily (a good old example) the Romans got attacked and were bleeded by probing attacks by the Carthaginians. Their own cavalry tried to stop them, but they did not have enough. Now Sicily was a big campaign, so you would have thought they would have had enough cavlary to protect the marching columns, but they did not.