Why is my index page not my highest visited page?

I’m just looking over my stats and I see that the index page is outnumbered by top level category page on my site for Unique Visitors.

I can see how Pageviews would be higher but why would Unique Visits be higher in a non-homepage if the homepage is the most likely starting point?

homepage is not the likely starting point for a lot of websites, because SEO changes this paradigm (now internal pages can have more traffic as more SEO optimized)

I forgot to mention: This is actually an internal website so it’s not indexed by the search engines.