And, in the course of developing his code, Samuel F.B. Morse studied the word usage and thus the letter frequency of use distribution for the English language and assigned his dot, dash accordingly. Thus the most frequently used letter "E" was assigned "." dit, the next most frequantly used "D" was assigned "." "."" dit dit", "S" was assigned "." "." ".' "dit dit dit" etc.
A genius at work.