Genetically women are hard-wired to be much more selective when it comes to sexual matters. Women, after all, must worry about pregnancy, and evolution punished promiscuity in women harshly. Since human females can become pregnant at any season of the year, evolution produced women who are cautious about sexual activity, who choose their mates based on a lot more than beauty or mere availability. A woman's sexual partner had better be a steady and responsible type who will be around in nine months and who can provide and care for any family that might be coming. As civilization has developed protections against pregnancy, modern women have become more sexually adventurous, of course, but that doesn't change the hard-wiring, nor the fact that most women want romance to play some part in sexual encounters.
One of the most illuminating letters I've ever seen about this was written by a lesbian to a gay news magazine. She scolded the editors this way: "Let's stop talking about sex in public places as a 'homosexual' problem—it's not. It's a MALE problem. Straight men would have sex in parks if straight women would meet them there." She's absolutely right; and note that no news story has ever complained about lesbians in the bushes.