Why are my iTunes factory equalizer presets all flat?
If you have your iTunes audio output set to go to an AppleTV, it will display all presets as flat. Change it to another setting, and the currently-selected equalizer preset will still display as flat. Choose a new equalizer preset, and it will look fine.

Our ATV is called "Living Room". So in the example here, I would choose "Computer", then choose a new equalizer preset, and it will work fine.