Higher clock speeds are absolutely still possible, just not in CPUs with high numbers of cores. More cores = more heat, and dealing with heat is one of the bigg

Higher clock speeds are absolutely still possible, just not in CPUs with high numbers of cores. More cores = more heat, and dealing with heat is one of the biggest challenges when designing a CPU. For servers, doing more things slightly slower is (usually) better than doing fewer things faster, so Intel usually puts core count over clock speed for their Xeon CPUs. For a desktop system that's unlikely to be doing more than 3 or 4 things at once, you can prioritize single core performance and higher clockspeeds. It's also considerably more efficient to have more slower cores than fewer faster cores. Reducing power consumption and reducing heat is a win-win in a datacenter.