I think it's because a lot, if not most, people that initally want to learn the guitar is because of the image. Especially for teen boys. So its natural for them to want to be a guitarist before a musician.

From personal experience, i initally started playing guitar because i wanted to be john frusciante. At 17, theory just looked like homework. I just wanted to get laid and have a reason to act like an idiot, really. I learned most of his solo stuff and came up with licks based on his style, but i did not start to look at theory seriously until i was around 24 (with plenty of time off due to personal ups and downs).

At 31 i can see how foolish and what a waste of time those years were. I think as i matured i stopped caring about the image. The love of music never left so now i take the time to appreciate why it sounds good when i fret certain strings, why a minor chord is called a minor, scales, etc. Ive ventured into other instruments since the language is universal.

I am not sure where i am going with this, so i will just say i dont fault people for not wanting to be a well rounded musician At first. After all, music theory are "rules" for something very abstract (manipulation of sound).

I say people should be free and encouraged to play for whatever reason they choose :)