Why did early transliterations of Chinese use unnaturally hard sounds?

The earlier transliterations (Wade Giles?) seems to have universally made Chinese Mandarin read harsher than it is. So “CHung” instead of the proper “Jiang” (with a french style ‘J’ on that).

Did Mandarin change, or were the early ‘foreign devils’ like Wade-Giles hard of hearing? Peking (PEE - KING) sounds distinct and much more constanant-al than the softer Beijing.