why keyboard keycaps are not arranged from A-Z?
In the era of typewriters when first it was invented the layout of the keyboard was normal and it was arranged sequentially from A-Z. As it was new for everyone all of their typing speeds were very low as days past by when the speed started to increase their raised a problem.
The typewriters have typebars (The part of the typewriter which hits on the paper to print the alphabet) it doesn't move and hits the same location while the paper keeps moving. As the typing speed increases the typebars gets stuck with each other as in the English language, there are tons of words which will have pairs of letter near to each other like 'in' etc.
So in order to solve this, manufacturers designed a new keyboard layout where they separated most commonly used letters and kept them far apart from each other. This gave birth to the QWERTY. The name of the layout has no relation to the logic.