A computer's components doesn't need constant monitoring. They're monitored by humans - if the CD rom drive breaks down, a human will fix it.
If an animal gets hurt, it's nervous system will pick it up and do the management necessary to direct resources to repair where it's hurt. Each part of the body requires some sort of monitoring system. The bigger the body, the more computational power must be devoted to body maintenance & monitoring.
A small brain vs body size means there's little "computational surplus", it's mostly used up for making sure the body processes are running, making repairs as required, moving hormones around, etc. A large brain vs body size means spare computational capacity is available for observable intelligent behaviour.
If an animal gets hurt, it's nervous system will pick it up and do the management necessary to direct resources to repair where it's hurt. Each part of the body requires some sort of monitoring system. The bigger the body, the more computational power must be devoted to body maintenance & monitoring.
A small brain vs body size means there's little "computational surplus", it's mostly used up for making sure the body processes are running, making repairs as required, moving hormones around, etc. A large brain vs body size means spare computational capacity is available for observable intelligent behaviour.
Anyway, that's my theory.