Cannae - why bother with the cavalry?

[Sardaukar]

Romans in Cannae deployed according to their doctrine. Doctrine is basically "how army is supposed to fight". Trying something that was not in doctrine would require lot of training pre-battle, otherwise it'd just drive army into confusion. It'd also require more experience among troops and especially bond and trust between troops and commander, usually created by succesful battles.

So, Scipio Africanus with his army could probably have pulled out something different, but consuls in Cannae didn't have the familiarity, ability or trust of the troops to try something out of doctrine.