Where's the bottleneck: PC hardware underutilized

I've read the "PC optimization guides" and previous posts about same. But that hasn't reached the crux of my question. I don't have the fastest video workstation and I accept that. But I'm puzzled why, by the performance metrics I see, my hardware is heavily underutilized. I'm only interested in rendering not previewing. Most of the time I see the following metrics in Task Manager whether I'm using AE's render queue or AME (I expected they'd be close and they are):

CPU: 25-35%

RAM: 65-95%

GPU: 0-3%

Why is my CPU hardly getting in the action? I thought about adding some more and faster RAM, but would that account for the low CPU use? Is there something else that could be throttling the CPU? THX.