“..it was quite common to abbreviate common names like William (Wm.) and John (Jn.) as well as many other words commonly repeated in documents and letters. Names were very commonly abbreviated, and not always the same way – this list shows “Charles” written variously as “Cha,” “Chal,” “Chars,” “Cha,” “Chl,” “Chle,””Chles,” and “Chls,” so it’s not as though the abbreviations were always standard. Diminutives of full names often become given names, but not necessarily because of misread abbreviations. I’ve met a few Beckys and Amys whose full names were not Rebecca or Amelia, for instance.”

Hope this helps you!

If you ask “Why?” about anything in the English language, the correct answer is probably “Because”.