If you use a keyword more than a reasonable number of times, the content fills up with it. Readers feel that while they are reading, get put off by the page and leave it.
That also tells the reader that the content was not written for them. Over recent years Google has moved to treat people who stuff keywords as spamming.
Here are a few ways to avoid keyword stuffing that you can put to work:
Write longer pieces
Use synonyms and words from the same word family
Use the equivalent English phrases
Use descriptive phrases
Use the keyword in page elements such as alt and title
