It sounds like, professionally, there's no reason to deny you. I have heard that they're only hiring people with degrees now.
However, as far as I know, they strive to have a writer base with diverse interests, hobbies and aptitudes. Perhaps your "niches" weren't ones they needed filled.
Several people who are writing there now, were denied more than once before finally "getting in"
You didn't say much about your samples (I forget if DS asks for writing samples) Make sure that they are written in third person and free from grammar and spelling errors.
You might want to "pitch" a different side of you, in case you have other skills or knowledge they may be looking for.
The other day they were looking specifically for people with genealogy experience. Livestrong writers have a medical background, Trails.com writers have "outdoor adventure" hobbies and like to travel.
Just try again, it's no big deal. That's what writing is all about. If you can't handle a rejected application then you do NOT want to meet some of the crabby editors.
Perhaps I shouldn't say crabby, they just fail to communicate like adults. I'm lucky my rewrite percentage is under 10% right now, but it's been like 2 years almost.
Good luck, don't take it personally either. Just play the game.