This is debatable because I dont know what you mean when you say they didnt know theory. Hendrix is a great example, supposedly he didnt know, but it is very clear he would play the pentatonic of the quality of chord he was playing over. Is that knowing theory? Or playing is playing the BB King box theory? Or is knowing the major scale theory? It's almost certain that the best guitarists that you're saying knew some of these things. So do you mean the nomenclature?

In Miles Davis' autobiography, Davis talked about how they jammed a few times. Davis would tell him to play a particular chord or scale, and Hendrix had no idea what it was at first, e.g. "try an E minor diminished yada yada there... a mixolydian scale would work on top of these changes..."

Once Davis taught him the concepts he got them immediately, or it might be a chord he knew and played, but didn't know the formal name of. So, he was a brilliant intuitive musician, but didn't have the theory chops of someone who attended Juliard like Davis.

That is what we mean by Hendrix didn't know the theory.

I mostly agree with this.

Like, I know what a secondary dominant is because I've had to use it in blues turn arounds- I didn't know that's what some folks would call it, but I knew that in the key of G, I'd often play an A instead of the Am.

And I think that the vocabulary should describe what folks do rather than the doings being driven by the vocabulary.

Most guitar players (and improv folks) that I know have much more theory that the folks who are reading but who generally don't think about what the function of their line is in a larger song.

If you're playing by memory and ear, you have to have some concepts because you can't just read a part.

Those concepts -are- the theory.

Right, you can be an incredibly articulate speaker without necessarily knowing the grammatical terms for the different parts of speech in each sentence.

I think there's a number of people who learned to play by ear who just sort of "internalized" theory without needing a formal curriculum.

They have taste for sure and an ear for a blues lick, but they don't know formal theory. It's like how my cat understands gravity but has no awareness of formal gravitational theory or the maths involved.

I'm not really tracking where your confusion is. You can very much so do or "discover" something in practice that a theory describes without knowing that theory. I'd say it's even very common to "know" certain notes/chords/whatnot sound good with others and not learn "why" until later on, if ever.

Anyone can clap hands and hum, the music isn’t the theory.