They way people go on about brushing teeth you'd think I'd have lost all my teeth years ago, but I still have them all and I haven't had a cavity for three years now, and one time they asked if 'd been bleaching my teeth because they were so white (I haven't).
But when I was a kid I was extremely terrified of going to the dentist and the fear lasted until my early teens. Treatment feels more like a punishment for not taking PERFECT care of your teeth, and then you're punished even more when your parents act like drill sergeants or won't let you eat candy.
I find my mouth is very sensitive to certain toothpastes and brushes. I have to use soft bristles brushes and hard bristles can damage tooth enamel anyway, and those potent whitening toothpastes will damage my whole mouth. Also instead of feeling clean and pleasant I feel like I've got freezer burn of the mouth for hours. Eating becomes painful, acidic or spicy foods cause all my taste buds to swell up, and my mouth feels really dry, which is definitely not good for dental health.
I don't know if that helps or anything but that's just my own personal experience and if kids associate brushing with something very unpleasant they're not going to want to do it ever.