Because our main role as bassists is focus on rhythm, chord tones and chord progressions. If you don't understand harmony/theory very well, learning the modes isn't going to help you with very much. More knowledge of harmony theory will go a lot farther... and you will learn about modes with better context of their uses as you gain that harmony knowledge. Most people that ask about modes are missing the information that is needed before learning about the modes.I disagree. Why not? There are a lot of modal tunes and songs (as can be seen in this topic for example). And why is this less important for a bassist than for any other musician?