One problem inherent in learning theory is it's plain scary! Unless you were forced at AK47 point to learn as a child it can be very daunting, especially if it's in aid of your hobby (folk music, blues, country etc.)and you also see that many great musicians can't read a note.
I had a neighbour once who would sit down at her piano at 11am every morning and play gloriously for an hour. From upstairs, I would try to predict what she might offer that day, Rachmaninov's "C#m"? A Chopin Polanaise? I'd get a book and read for the hour while enjoying her offerings, always impressed with her timing and dynamics - the whole ball of wax. One day there was a birthday party for a mutual friend in my neighbour's apartment, and while the candles were being blown out, I noticed my neighbour madly searching through her voluminous pile of sheet music for 'Happy Birthday"!! "Richard", play it, quickly, she asked," I couldn't believe that she was so locked in to her music that she couldn't play something that simple by ear. Over the next few months we talked a lot about music, and I found that along with extensive piano lessons as a child she'd also been indoctrinated about "good and bad" music by her parents and music teacher. I started bringing albums over for her to listen to - stuff like "The Hot Five", "Bix", Ellington, (I knew enough not to try Bill Evans or even Art Tatum at that point). She hated it all. Once I tried to get her to listen to "In a Mist" and went through all the stuff about Bix mixing styles etc. She just said "I think that's SO vulgar"! Sadly the 11am concerts stopped. I never asked, but I think she felt that since I loved "that silly noise" as she called (pretty trad) jazz, I couldn't possibly appreciate her renditions of the classics.

If I'm working with students on any kind of theoretical approach, it's ALWAYS after we've spent a substantial amount of time on learning to play by ear, learning to improvise AND learning to play with others (on their terms). Good jams are one hell of a lot of fun. I don't use any books on theory when I'm working with neophytes, just get 'em to memorize "Do Re Mi etc", then put the note "C" to the "Do", and then put the number "1" to the "C" and the "Do". It's much less intimidating, and pretty soon they know that a lot of folksongs, blues, and country songs are just good ol' 1, 4, 5.

Rick