AmE pronunciation of 'cliché' vs 'niche'

I have noticed that some Americans (not all) pronounce the word 'niche' as 'nitch' (IPA /nɪtʃ/) rather than as 'neesh' (IPA /niːʃ/).

niche Pronunciation: /niːʃ/
Pronunciation: /nɪtʃ/
(Oxford Dictionaries)

Why do these same people not pronounce 'cliché' with a "tch" (IPA /tʃ/) sound?

Both words are loanwords from French, but the treatment of the "ch" sound seems to be inconsistent. Is it due to the difference in accentuation?

Also, which groups of people use 'nitch' as the pronunciation for niche?

Is it wrong or can one argue for it?

As a Brit, unsure as to internal American differences in pronunciation, I was wondering if nitch is more of a western pronunciation. I have heard that it becomes more like British English as you go East.

OED has for niche

Brit. /niːʃ/ , /nɪtʃ/ , U.S. /nɪtʃ/ , /niʃ/

so both sides of the Atlantic have both pronunciations; but which is more common is reversed. OED also has alternate spellings from the past:

16 neece, 16 niece, 16 niech, 16–17 neech, 16–17 nice, 16–18 nich, 16–18 nitch, 16– niche.

Jonathan Swift, 1733:

If I can but fill my Nitch, I attempt no higher Pitch.

For cliché

/kliʃe/ /ˈkliːʃeɪ/

Apparently no /tʃ/ version