I would wager that in each of the cases, you wrote in a different voice. You automatically adapted your voice to the situation.
I often say that I can write for anybody, as long as I know their vocabulary. I don't need to know how to perform heart surgery to write about it. I just need to be able to decode the language. Same with tropical orchids or pet turtles, local politics or the pharmaceutical market. Each of these corners of the world has its own language rhythms, its own code. You break the code and you're in.
I see writers all the time on the Internet worrying about this thing called voice: "What is it? How do I get it? Why does it matter so much?"
My advice is simple: relax. Anybody who writes anything ALREADY knows how to adapt their voice, because you do it subconsciously every time you open a new file or e-mail. You think about who you're writing for and what you need to say, then you pull up the necessary vocabulary in your brain, and you get to work.
I think it's the same with novels. Each genre, each audience, has its little mysteries and codes and lingo and slang. As a novelist, you don't need so much to plumb the depths of YOUR soul to discover your voice. No. You need to plumb the depths of YOUR READERS' souls and tap into their inner dialogue. This means, if you're writing for kids, you read what they're reading. You listen to kids. You absorb their experience, their vocabulary. If you're writing police procedurals, same thing. And same thing with women's fiction.
That's where you'll find your voice.