The English language has a great amount of borrowings from French. But why aren't such letters as "ç"(façade) and "é"(café, protégé) changed if they don't exist in the English alphabet and there are "c" and "e" only? Also I have a question about the surname Brontë (I mean Charlotte Brontë). Again English doesn't have a letter like this (ë). I looked up the etymology of the surname. It told that the word "Brontë" derives from Ancient Greek and initially meant "thunder". But "ë" looks like a French letter, though Charlotte Brontë didn't have French roots if to believe Wikipedia and was born to British parents. So what is French-like letter doing in the British surname of Greek origin?
The use of original spelling of words (especially of French words) was associated with a high level of education and knowledge of foreign languages. English doesn't use many accents, but it is considered correct to do so in borrowed words. So, while both "Facade" and "Façade" exist as correct spellings in English, the second spelling suggests that the person is sophisticated enough to know French and to care about the detail of the ç. In a similar way, a "cafe" /kaf/ is a place where you can buy eggs, sausage and chips; but a "café"/kafei/ you buy "latté" and "pâtisserie".
In general, English spelling doesn't follow the sound of the words, but is based on the origin. It is natural for English people not to change the spelling of a word, even if the sounds of the foreign language aren't the same as in English. For example, we might use "ciao" /tshau/ to copy the Italian pronunciation of "c=/tsh/" and keep the Italian spelling too. We neither spell it as "chow" nor pronounce it as /siao/
There is a element of showing off, and snobbishness about using accents in words. Similarly, English speakers may attempt to copy the pronunciation of foreign words, and there is an element of feeling superior to others by using "correct" foreign pronunciation. Using accents is a way of signalling a high level of education.
The Brontë name is Irish in origin "Pronntaigh". By 1830 it had been Anglicised to "Brunty". The father deliberately changed it, apparently to make it appear sophisticated, elegant and Hellenic.