Do you think that this is a result of teaching as a function of the role that the instrument plays in popular music?
Bass rarely plays chords in popular music, so why teach harmony? Bass rarely solos in popular music, so why teach melody? What does that leave? Rhythm, locking in with the drummer and "groove"!
Of course, if you want to be proficient in music, you should learn it all and why should your choice of instrument limit your knowledge of music as a whole?
I am always surprised by those who refuse to learn how to read or learn any theory inciting that it will stifle their creativity. How can having more knowledge prevent creativity? Like you mention, they are two separate entities (learning and performing/artistic expression).