Because this is Apple. Audiophiles are supposed to use their own hardware (a DAC, an amplifier, headphones or speakers). Sound engineers are supposed to use their own hardware and software with low latency drivers and output algorithms, bypassing OS X completely. Non-pro consumers are not supposed nor expected to mess with the way the MacBook is designed to sound. I'm sure dozens of Apple's engineers spent dozens of hours designing the audio to sound and perform exactly this way. A speaker is a pretty fragile thing and "spicing up" the sound a bit too much can easily damage it. I'm not saying you're doing anything wrong, but in my opinion audio systems and equalizers are a thing better left alone by the general public.
