Why do most English speaking people "forget" how to say foreign words?

ya really i mean honestly Americans are the worst at pronouncing foreign words. like the name ahmad in arabic how did they make it "akhmad" or akmad? the kh is a letter used in Arabic Hebrew and i think Spanish. it comes from the back of the moth beginning of the throat but the letter isn't even in the English alphabet so how did "ahmad" become "akhmad"????? and there are words with the letter h that they just totally ignore as if the letter isn't even there. i'm with you i pronounce the word as it's is. except if the language has a sound i've never used but i still get it as close as possible.