I have often asked myself this, especially as I was raised in a very conservative Christian home.
I must say that all the potential answers I have come up with "work" for me, I find them all quite acceptable.
Obviously, I accept karma and that sort of speaks for itself. The first time I really started studying the Dharma I just felt (pardon the cliche) as if I had come home.
Then, on another level I suppose that my training, my education, my personality also all point towards a largely rational, even scientific approach to life, and again I find on that level that the Dharma makes sense to me, it does not really (with very few exceptions) ask me to accept things that causes cognitive dissonance such as certain other worldviews require.
I have also had the benefit of having Buddhist friends from an early age, I find the art and most of the cultural attachments absolutely beautiful, and the whole message of peace and compassion towards all sentient beings all resonate with me.
So, while I am immensely grateful for being "here", I am not really surprised