Once upon a time, when typewriters were new there was no standard for letter layouts. Naturally, the alphabetic order was tried, along with some other crazy and now dead layouts, but there was a problem: writers on these layouts were typing too fast. The keys would strike at the same time and the typewriter would jam. So with this in mind QWERTY was invented. The letters were jumbled around until the keys did not strike each other and thus the standard was born.
QWERTY is not designed with the health of your hands in mind. Knowing this, August Dvorak designed a new layout with efficiency and ergonomics as his goal. The Dvorak home row (AOEUIDHTNS instead of ASDFGHJKL;) consists of the most commonly used vowels and consonants in the English language with the vowels on the left-hand side to promote an even distribution of work between the hands (unlike QWERTY which forces most work on the left hand). The top row, the second easiest row for your natural reach, contains other common letters and symbols, while the bottom row (the hardest reach for your hands) contains the letters and symbols least used.
Simply put, QWERTY is an ancient layout that had very little thought behind it. It was obsolete even before typewriters became portable.