Am I missing something, or am right in making the assumption that the WordPress core just doesn’t facilitate sub-pages on the main page of the blog?
You are correct – I think technically every other page is a subpage of the main page.
In the Parent page option, Main Page (no parent) is the option.
Alternatively, you could create a new main page (main2), then use the WordPress options to set the main page to the new page (main2) and have subpages?