Girls use them all the time because they don't care about the risks, are uninformed, or think it can never happen to them.
My cousin and I have the same basic ethnic make up. Half Native American, half Irish. I got the pale Irish complexion, whereas she got the darker Native complexion that allows her to easily tan, as opposed to my burning and freckling. Because of this, she feels that she is immune to anything harmful when it comes to tanning. We discussed it once, and I told her that just because I am more susceptible to burning doesn't mean she can't get cancer or something. She said, "I don't care. I'm half Cherokee, so I should look half Cherokee!!!"
Her appearance is more important to her than her health.
So don't be fooled into thinking that just because it is popular, that there are no risks. You're getting good advice here, just make sure you do some of your own research before making any rash decisions.