Top Primary Keyword Not ranking? Do you know why?

A primary keyword, also known as a focus keyword, is the major search phrase that a website targets. If a top primary term isn't ranking, it could be for various reasons:
Competition
Keyword difficulty
Content quality
Backlinks: A poor backlink profile can harm your rating.
Website age: It may take some time for new websites to rank on Google's first page.
Indexing issues

I would say you should build some quality backlinks, it sounds like you have covered everything else, so maybe the missing piece.

Businesses will often encounter this ranking issue when targeting high-competition keywords with a website with a weaker backlink profile. That's why we recommend solving this issue by pivoting your keyword targeting to lower-competition, long-tail keywords.