Most guitarists make money by performing AND teaching.
Of course, there's people like John Williams or Bream, who don't really have to teach on a regular basis, because they make a very good living just touring once or twice a year... except that Bream doesn't tour anymore, not that I know of
like Owl said, if they record some music also, that becomes an additional source of income.
A few years back, in the 90's, at one of John Williams' concert in Chicago, at Orchestra Hall, I knew the person that signed Williams' check for the night. It was $30,000. I know, I know, but please understand two things: one, it was JOHN WILLIAMS, and b

, there are, I don't know, at least five thousand seats at Orchestra Hall - the cheapest ticket was $48 I think. You do the math.
But it is not good to use John Williams as an example because he is an exception.
I think the amount guitarists make each year depends on each individual: their level of playing, their popularity, the opportunities they find to play, their management, and so on.