Before America and before American dollars the premier currency was the Spanish eight reales or Piece of Eight. Although one singular coin it was called a piece of eight because it was often cut into eight pieces, each piece being called a bit worth 12½¢. When the United States mint opened in 1792 two bits became a quarter but Spanish and other currency still prevailed as it took around two decades for American currency to meet demands. Besides the Spainish many other Eastern hemisphere countries do not have a 25¢ coin. The British pound does not, the Euro does not which brings us to the $20 bill.

Like the quarter, a $20 note is what Americans were used to using. Also pretty much every other country use a $20 note, I am not aware of one that does not.