I think it's because these "h"es are silent in (most?) dialects of English, so both spellings would result in the same pronunciation. English doesn't really hav

I think it's because these "h"es are silent in (most?) dialects of English, so both spellings would result in the same pronunciation. English doesn't really have a 'kh" /x/ sound, or an unaspirated k, or an "ahn", or a "dh" sound. So Kahn and Khan both get read as /kan/, Gandhi and Ghandi both get read as /gandi/. If anything the "h" just seems to hint that the vowel isn't pronounced /æ/. So folks remember that there is a silent h but not where it is. Of course many Indian languages have aspirated and unaspirated "d" sounds, for example, and this is also reflected in the English dialet. But most of us English speakers can't hear the difference very well even if we concentrate.