Did your date look down a lot? Laugh nervously? Seem to take a while to warm up to you? A shy date will almost certainly not make the first move and may withdraw slightly from your advances. Even if you're sending out clear "I'm into you" signals, the shy gal who fears rejection would rather avoid a potentially amazing smooch than take the risk of being turned down. Give her a little more time to get comfortable with you, and next time make the first move.
A first kiss may not seem like a big deal to you, but if your date is very religious or has conservative values, she may take any kind of physical intimacy seriously. It should become fairly obvious early on if religion is an important part of her life. Ask about how her faith (or upbringing) plays out in her dating life. From there, you might need to re-evaluate your expectations...or compatibility.
She doesn't think you're interested
You're pretty sure your date is into you - but have you made it clear you're into her, too? You may be inadvertently keeping her away by sending out subtle "stay away" signals with your body language or tone. Are your hands shoved down into your pockets? Your arms crossed in front of you? Have you pulled away from any accidental touches or avoided eye contact? A first kiss usually comes after some other casual physical contact, so don't shy away from bumping knees under the dinner table or lightly brushing arms when you walk.
She isn't interested
Sometimes when you feel like you're being blown off, you are. Stick around for a second date (assuming one happens), double-check your breath and see if your chemistry doesn't improve the next time around. If a kiss doesn't seem forthcoming after that, your date may just be killing time with you. And in that case, you should feel free to give her the kiss-off.