Because static scheduling is terrible for non-DSP and non-HPC loads like the typical server or desktop application where the control and data flow is very input

Because static scheduling is terrible for non-DSP and non-HPC loads like the typical server or desktop application where the control and data flow is very input dependent. Until recently DSP and HPC were a tiny fraction of the market so architectures capable of dynamic scheduling dominated even those markets as they had more investment. With GPUs of course things have changed and in fact GPUs relied more on static scheduling, but even there as they expand to more varied loads, they are acquiring more dynamism.