Basically because the patterns are transferable between keys and strings . For example , the Cmajor scale with the root on the 6th string at the 8th fret , move it and use the root note at third fret of the 5th string or the fourth string at the 10th fret and the pattern remains the same except for the second string , because it is tuned to a 3rd above the 3rd string and not a fourth like all the rest