Norman scribes and authorities in England favored Norman French–style spellings with C, which worked fine for appropriate-sounding words like “cat,” “cease,” “city,” “cow,” and “cut.” But, as in German, the scribes also faced English pronunciations that didn’t work for C, pronunciations with a “k” sound before an E, I, or Y, as in “king,” “Kent,” “speaker,” “rocky.”
Simplicity of use may be the reason why K became favored over C in transliterating foreign words that have flooded into English since the 1600s, often as by-products of British colonialism. These aren’t just words like “ketchup” and “kiosk,” with problematic vowels, but also: kangaroo, koala, karma, karate, kung fu, karaoke, kow-tow, kumquat, skunk, polka, mazurka, and many others that could have taken a C.