Many workloads still are (and likely forever be) single threaded. For example, Javascript performance (for web browsing) is 100% single-threaded. Most programs also have a main thread that relies on single-threaded performance and just assign workloads to new threads as necessary.
https://en.wikipedia.org/wiki/Amdahl's_law
But again, multithreaded benchmarks will also say the same thing as the single-threaded ones on all modern platforms (Cinebench single and multithreaded scores have a R^2 of over 0.99 once corrected for the number of cores, same as Geekbench). All of these platforms handle multithreading very well. This really becomes a concern when you scale upwards of 100 cores on shared memory architectures. Not an issue at all on consumer computers.
Cinebench R23 is already ported to Aarch64 on macOS, so we'll see the results soon enough. Maybe once those results are out, the "Geekbench is bad" crew will turn into "Cinebench is bad" crew