What would be the benefit? You don't need a 10GHz processor to browse the web, or edit a spreadsheet, and in any case things like that are already multi-threaded.
The current direction of adding more cores makes more sense, since this is really what CPU intensive programs generally need - more parallelism.
You technically don't even need a 300MHz processor for the use cases that you name. But Intel and others kept developing faster CPUs anyway.
Single core speed is absolutely a thing that is needed and preferred to multicore. That's why we have avx, amx, etc.
For parallelism we already have SIMD units like AVX and well... GPUs. CPUs need higher single thread speeds for tasks that simply cannot make effective use of it.
Because someone decided to write all the software in javascript and python, which don't benefit from the added cores.