I used to have pin straight hair. As in, I was a flower girl for a wedding and they tried curling my hair...it took several hours of curling, spraying, curling, spraying, curling, spraying, until right before the wedding and all the curls fell right back out not long after the wedding was over. It wouldn't hold a curl for the life of me!
When I got older, I started getting these kinds and twists in my hair. If I don't blowdry my hair after a shower, sections of it will start to curl, but not enough that I could actually style it to be curly or even wavy. It's really annoying. Most times, I either put it up or straighten the parts of it that need it.
I think girls want the straight hair for everyday because they like it, but when it comes to special occasions, curly hair is so "different" and can come off feeling fancy and special, too. It's the same way that those who where their hair curly on a regular basis can get a confidence boost from straightening their hair every now and then.