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