The front page is filtered so that it doesn't show posts with no upvotes, thus sparing you from spam, unflagged pron, etc. (at the moment, snaps require three upvotes to be shown on the front page)
The best way to see the brand-new stuff as it's posted is to use your Home feed. If you follow the tribes with the most posts--that's the ordering on this page--or at least the ones that most interest you, you'll probably have more activity on your feed that you can keep up with. Since most snaps in the niche tribes are also posted in one of the large tribes, visiting the snaps that interest you is a good way to locate other tribes you might not have known about.
And the best way to get new content onto the front page is to upvote good snaps you see on your home page.
Hope this helps!
Not sure if you saw it but /u/gladsdotter replied with this.