Why is the correlation of my server's load average stat much lower than the server's CPU usage stat?
Please keep in mind that questions in relation to system metrics are best handled by a systems administrator with the skills, training, and expertise required to provide answers for you.
The key to beginning to understand this is to know that CPU usage and Load Average are not the same. Although they often correlate closely, they measure different things and can diverge.
Specifically on Linux, the load average tries to be a resource to measure system metrics rather than just CPU metrics. More can be found about this in the following resource:
Linux Load Averages
It then becomes possible for the load average to measure both higher, and lower than the CPU usage metric.
In the case where the load average is lower than the CPU usage metric, it means that there are short lived tasks that are using a lot of CPU, but are short enough that they are not captured by the load average measurement. The following resource explains in more depth and provides a proof of concept script:
High CPU utilization but low load average