Why are "gh" not pronounced ？

Tanaka? OK. Anyway, that's the Norman influence. 8 could be spelled "octrain", & phonetically "fight" could be "fite". But, the sound in the ear has an influence. Like multiple spellings for "there". It's pronounced the same, & spelled different for they're different meanings. English is a Germanic language with French influence. The "gh" sound was dropped in Middle English.

It was pronounced at one time but has either gone silent or changed sound. The sound used to represent what is written as "ch" in languages such as German or Polish.

Just because.Removing the letter would make the words even more unreal.

well first off you have this in the wrong category.  In this category we are talking about the American Soap Opera General Hospital.  You might look under Education

English is an evolved mixture of many other languages.  You can find words with French, latin, Celtic, German, and other influences.  Sometimes the same word evolved from multiple other languages' influence.  It's why English is inconsistent and kind of rule free.

In this case, these words evolved from predecessors with a gutteral noise, and as English incorporated those words, they changed and evolved because English lacks that gutteral noise.  The gh kind of stood in.  

We English speakers have been asking the same questions for centuries! English is chock-full of annoying inconsistencies like that. It has way too many arcane rules and contradictions,... but it is what it is.😏

If you google the etymology of these words you'll typically find that they're derived from older words with a pronounced "ch." 

For example, the etymology for "fight" is as follows: "Old English feohtan (verb), feoht(e), gefeoht (noun), of West Germanic origin; related to Dutch vechten, gevecht and German fechten, Gefecht." 

The reason for dropping it is presumably that the German "ch" sound does not exist in English. Most native English speakers will replace it with an "h" sound if it precedes a vowel and drop it if it follows one as in these words.

More generally, spelling inconsistencies in English exist because it was originally a synthesis of older versions of French and Dutch, two languages with very different spelling systems, and it took many centuries for spelling to become standardized. This was further complicated by the many words borrowed from Greek and other languages. And the pronunciation of words changes over time as well.

Your English seems pretty good to me btw.

Since much of English is derived from Anglo-Saxon "gh" represented a sound in Anglo-Saxon, the pronunciation of which has been lost over time.  However the spelling was kept. 

English is not logical. Gh is f in laugh and enough.

English is not a phonetic language.  That means that there is no consistent connection between the way words are spelled and the way they are pronounced when spoken.  It's just the way it is.  There are some pronunciation rules but they are not consistent and there are many exceptions.  Some languages, like say German or Korean, are phonetic, which means that if you know the spelling then you know the pronunciation (and vice versa).  That just isn't the case with English.