Simple wikipedia seems like a good source to explain this

https://simple.wikipedia.org/wiki/Nigger

> However, in the late 20th century, the word was seen as a hurtful racial slur in English. It was called hate speech. "Nigger" was seen as very offensive to say or hear which caused many to not use the word at all. They instead called the word "The N-Word". It is said with a "hard R", because the word ends in 'er' instead of 'a', as in the word "nigga".

Its in the Spanish word for black, it is taboo enough that people generally don't write it.