It has been theorized that childhood spankings lead to a focus on sexual spanking later in life. It makes sense to me. You're held in a vulnerable position, buttocks exposed, while a private sensitive part of your body is touched and struck. The rush of blood to the genitals can lead to physiological arousal, even without psychological arousal. All the while you're being told that you're being spanked for your own good, because they love you.
I can definitely see how the physiological arousal combined with the emphasis on spanking being a loving action could lead to a focus on it in sexuality later.
Were you spanked as a child? Do you think it had anything to do with your enjoyment of spanking in sex?