What Tibmeister said, but ignoring non-run states, most of the difference comes from ESXi CPU Usage being a qualitative counter that takes into account CPU frequency to approximate throughput. Most OSs default to utilization (i.e. anything but idle), so that would under-report due to Turbo Boost (and even if they would _want_ to use frequency information for a usage like counter, the necessary information for that isn't presented to a VM by default).
I do explain it in some detail here (~15-50min): https://via.vmw.com/MCL1635
