I get this question a lot. It shows a lack of understanding of sex so profound it saddens me. My friend has an easy answer to this one: "You like vaginas, right? Sheep have vaginas." I feel this sums it up pretty perfectly, but I have more to say on the subject.
Sex is about connection. The sex acts we do and the tools we use to do them (toys, tongues, fingers, dicks, pussies, the force of our energy, our voices, our words and everything else) are about furthering this connection. Our bodies have nerves, and sex engages those nerves...but the reason we fuck people and not sit alone and use a vibrator or our own hands or a fleshlight is because we want to experience something with another person. Sex is mutual.
I want to share that connection with people I'm attracted to. I'm attracted to women. I like the way women smell, the way they taste, the feel of their breasts and butts and skin and lips and the clenching of their muscles around my fist. I like women's energy. What turns me on and brings me to orgasm isn't just a series of sensations but also the entire experience of sex with someone else - I've gotten off with all my clothes on just from making a girl feel so exquisitely good I can't help but share it with her.
Feeling like a hole or a dildo or a detachable, interchangeable sex part isn't hot. Feeling wanted and wanting someone back is hot. If you want to have good sex, you have to learn how to connect with other people. This isn't rocket science. Stop pretending you don't understand.