Yeah, it’s the real world tasks that GeekBench tries to simulate that don’t tend to scale linearity with processor count. A lot of software does not take good advantage of multiple cores.
I use a few 32 and 64 core machines for build servers and file servers, and while the 64-core EPYCs are not twice as fast as the 32-core ones due to lower overall frequency, they're 70% or so faster in most of the things I throw at them.
I was under the impression that all of their multi-core tests were "run N independent copies of the single-threaded test", just like SPECrate does.
It sounds pointless to come up with synthetic benchmarks which emulate software that is not able to handle hardware, and then use said synthetic benchmarks to evaluate the hardware performance.
Most consumers are software aware, not hardware aware. They care what they will use the hardware for, not what they can use it for. To that end, benchmarks that correlate with their experience are more useful than a tuned BLAS implementation.