It’s there, it’s just not on the B string. The bottom diagram (CAGED patterns) starting on the 5th fret E string … C is played on the G string. You could play it on the B string instead but would create unnecessary finger stretching.
If you wanted to play G major in open position then you would use the diagram starting on the 15th fret an octave down so that it starts on the 3rd fret instead. The 12th fret in this case would become the open strings.
Hope that makes sense.
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