The online check-in and kiosks are optimized to check you in. That is basically all they have to do and are -- generally -- very fast at doing a limited number of things.

On the other hand, the agent's computers have to do just about anything related to airline reservations and ticketing. Therefore, it usually takes more keystrokes to do the same thing. As the AA agent above pointed out, agents are often checking your reservation to make sure that it's okay, you have the best seats, you're on the upgrade list (if appropriate), that you're not going to misconnect (if your flight is late), and a whole host of other things.

At least, the computers have a GUI (windows-like screens) these days. Ask some of the older agents about remembering native SABRE commands. But many of them were quite good at it!