There are lots of English conventions and that is certainly one--no more that 2 of the same consonant in a row. Since you can possibly pronounce it, and written language is just a graphic translation of speech, three consonants in a row doesn't make sense. Similarly, "u" has to follow a "q" in English. Modern use does allow spelling of some foreign words without the "u". Don't really know why it is allowed with Arabic since the alphabets don't have a one-to-one relationship any more than Cyrillic does to English. On the other hand, advertisers spell anything anyway that they want, but those spelling remain substandard or unacceptable.