ranking on a main keyword but no long tail

I have a site that is ranking well for the main keyword, but somehow the site is not receiving any long tail traffic for the content. I did backlinks mainly to the main page. Is it necessary to have backlinks to every page you want to rank now?

if you want to rank inner pages, you need to build backlinks to them

How old is your site? If it's young, usually you'll start ranking for your main keyword (I assume you're targeting that one in the home page) and then for the long tail. At least that's how usually go for my sites