Grammer and good sentence structure goes a long way.

Let me see if I can understand:
Your asking why people must turn on hardware acceleration?

Because todays CPU's can't handle the load of rendering gfx in addition to sound, physics, windows, etc. So, the gfx rendering is sent to a specific piece of hardware so the CPU can process other data, the GPU (located on a video card). Without hardware acceleration, the CPU handles everything, bogging it down by a considerable amount.

In addition, some gfx features can't be rendered by the CPU (which uses software rendering if hardware acceleration is turned off in dxdiag) such as pixel shaders.