(This is for females answering about their own motivations for anal sex. I think we can tolerate males reporting why their girlfriend etc. was motivated by anal sex, but, please, no answers from males about why they want to fuck a woman in the ass or similar offtopic.)
To women here: why do you have receptive anal sex, especially, why did you try it?
You wanted to experiment? To please your husband/boyfriend? To preserve your hymen? To have sex without risk of pregnancy?