Asking out of curiosity, and probably won't know what to do with this information, but for say E standard on a 6 string. Octave notes are up 2 frets, skip 1 string for strings E through G, but once it reaches the octaves on the two high pitch strings, it's now up 3 frets, cross 1 string. Why are guitars set that way? Wouldnt it have just been easier to make all octaves on the guitar to follow the "up 2 frets, cross 1 string" formula? So then E standard might be "EADGB#e#"?
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Convenience. The major 3rd between the G and B strings makes it easier to fret diatonic chords. Many musicians agreed that it was easier, so it became the standard.
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Quote by Axelfox
Easier to play chords. Try playing a barre chord rooted on the 6th or 5th string with evenly spaced tuning - EADGCF
There are, as you'd expect, some reasons for the current tuning. There are also some compelling reasons for other tunings, including perfect fourths or fifths (which extend the keyboard's reach), and then there's New Standard Tuning. Rather than ask on a forum, do a bit of research. Google is your friend. 
As the others have said, it is for convenience of fingering the maximum amount of useful chords.
There is a limit to how far the the average human fingers can stretch, and the majority of us only have 4.

Do some Net searching on the history of Guitars and Lutes etc. It is very interesting, and there is a plethora of information.
Last edited by Vreid at May 18, 2017,
With standard tuning, the pitch produced at any fret on the treble string is 2 octaves above that same fret on the bass string ... so barre chords across 6 strings become easier.

Ultimately the way you tune te guitar affects how many semitones the change is across adjacent strings at the same fret.  These all add up as you go across strings.  As you go along a string towards the body, the semitone count increases.  Towards the nut, it decreases.

Every scale and chord is made up of intervasls (semitone distances), and so, by adjusting these distances with the tuning, these shapes all change. Some may feel easier to play than others.