Why do we spell Czech in English with a "cz" while Czechs themselves use a "c" with an upside-down caret - i.e., Cech?

Before the 14th c. the Czechs also used the English spelling where the digraph (meaning a pair of letters that represents a single sound) "cz" stands for the "ch" sound. It was Jan Hus who modernized Czech spelling by replacing these digraphs - which occurred wherever a distinctive Czech sound did not have a corresponding letter in the Latin alphabet - with diacritics, the little upside down carets which adorn c's, r's, s's, and z's in Czech to produce the ch, rzh, sh, and zh sounds. English appears to have adopted the old Czech spelling - likely because the word entered English before the 14th c. - and couldn't be bothered with Czech spelling reforms. Interestingly, the Poles have maintained many of these old digraphs and thus they also write Czech with a "cz". Languages other than English have more sensibly decided to spell Czech using their native phonetic system so that people can pronounce the word correctly without tripping over an ancient and foreign spelling system.