After you've been writing for a while, eventually you may start to notice things that your stories have in common: character archetypes, physical traits, pastimes, belief systems, that sort of thing. You might not mean anything by it, or you might just be writing what you know, or you might be purposefully casting these details in a positive light within the context of the story to show that, hey, XYZ isn't that bad, even if you might think it's a little weird or unusual.
TV Tropes calls this Author Appeal, and depending on how it's handled, it doesn't have to be a bad thing. Think of it this way: You write what you know, creating settings that appeal to you, the author. The main character might be someone you'd like to know, or even You But Better, and the place and time where he lives might have some element to it that you find interesting or appealing enough to want to explore in detail via your fictional medium.
Improperly handled, a story where (for example) most everyone is a bisexual nudist who practices BDSM and eats pepperjack cheese on everything and anyone who doesn't is a horrible person who dies horribly could be a turnoff for most readers (except for a small portion of potential readers), and make your story ripe snark bait because OMG LOOK HOW WEIRD THIS AUTHOR IS. I've seen this level of ham-handedness in a number of works--mostly fanfiction that is a step or less removed from a self-insertion fic, but some original fiction as well. Basically, if the main character has exactly the same tastes and ideas the author holds most dear, and everyone loves them for it or is inevitably coerced over to their way of thinking (or dies during the course of the story)... yeah.
However, properly handled, elements of author appeal can form a subtext that remains exactly that--subtext-- without beating the reader over the head with whatever notion of ideal beauty or perfect society the author holds. Such elements can become topics for which the author is well-known without ramming them down the reader's throat. The author likes curvy women and writes books featuring them? Great--those books will attract readers who also like curvy women. The author likes baseball and writes books with baseball storylines? Great--other baseball fans will want to read them.
As I look back at some of my current and past works-in-progress, I've noticed that I do this, too. For example, I have a thing for tall, intellectual male characters with long, slender fingers. (This may be connected with my love of Sherlock Holmes stories and later love of the character of Severus Snape in the Harry Potter novels.) As a result, The respective male leads of a handful of my stories are super-smart, often described as tall, and I give them slender fingers. This is neither a good thing not a bad thing, exactly, just a Thing. My heroes also tend to use their brains rather than punch their way through a problem. (I blame MacGyver for this.) Again, neither a good thing nor a bad thing. If I write about characters that appeal to me, I will enjoy writing them, and with any luck I'll find readers who also like tall, intellectual heroes with slender fingers. If I write a character that I think a certain demographic will like, and I end up hating that character, the story probably won't ever get done--or if it does, it will feel half-assed because I was just writing it to get it done rather than because I enjoyed it.
I admit that I don't get the Twilight books. Vampire romance stories don't appeal to me. Stephenie Meyer has piles of fans who read her books and would like to take Edward Cullen home with them, dietary concerns aside. That's fine. She's found an audience for her author appeal. I think that chances are good that most authors will find an audience for what appeals to them as well, if they present it properly and look hard enough.