These 5 links below the « blog » menu link are categories. When you click one of those, you enter the category and get access to all the content classified under it.
So, because the categories are in the menu, and the menu is ever-present across the site, it means that Google-bot only needs to hit any page on that site, start crawling and find category links (first click) + all posts within each category (second link).
That is the easiest way to flatten a site’s architecture, but it’s not enough.
Because similar to blog feeds, categories usually hold only 10 posts on the first page, and after that, the pagination starts.
So, if for example, a category holds 100 posts, then there are the first category page + 9 category paginated pages.
The problem here is that most themes wouldn’t show internal links to all 10 of those pages, but instead to only 3 or 4 max.
For example, when I click on the Software category on the supported StartupBonsai, I see that there are 40+ posts in total and 5 category pages.
But there are links only to 4 of those, leaving one paginated category and its content orphaned and invisible to Google-bot.