Look at the top of this page: Home » Docs » Breadcrumbs. Three crumbs, none of them a link to this page.
The last crumb is this page’s parent section, not this page. Hugo’s .Ancestors excludes the page itself, so the trail is built from what is above you and stops there. The page you are on is named by the <h1> a few pixels below — repeating it as a self-link added a heading and a dead link and told a visitor nothing.
The JSON-LD is not quite the same shape. Its BreadcrumbList does carry this page as a final ListItem, but with a name and no item — the standard pattern for the page you are already on, and what keeps a breadcrumb rendering under the search result. View source and compare.
Go back up: Breadcrumbs is one level, Docs is two.