Because a CPU is more complex, you have also to look at the other parameters, like the RAM clock (that’s handled by the cpu), the instructions set, the other connections BUS, etc… obviously if we are comparing a same x86 architecture and not ARM vs x86 or other RISC vs CISC.

Using only the clock is like comparing two cars using only the number of horsepowers without the weight, aerodynamic, frame, etc…