I'm guessing the reasoning behind that statement is the power consumption. The higher the clock rate of a core, the more power it consumes and the more heat it

I'm guessing the reasoning behind that statement is the power consumption. The higher the clock rate of a core, the more power it consumes and the more heat it dissipates. If you don't slow down each core in a crowded multicore, things might heat up too much and melt down. Until we get some other semiconductors that can withstand the heat, I'd say that's probably going to happen.