TMI time!
I used to have loads as a kid. One turned up after cutting my hand falling over in a playground, on my palm. It then spread - eventually I had two on one thumb, one on the other, a couple on the finger pads and the original one had formed a cluster. I got verrucas too, it was pretty depressing.
Used all the usual bazooka-style remedies around at the time, which really didn't get me anywhere (the one I had required filing, soaking, reapplying every day), and the freeze-cans you could buy were a bit too much to use on my hands given the placement of my warts, and on my verrucas they just blistered the skin around them, leaving the verruca happy as larry surrounded by red, angry sensitive new skin.
Anyway, I think a mixture of two things happened:
One, I broke my arm, and the cast I think somehow starved some of the warts on my palm of oxygen or something, or just made the environment a bit too moist and stuffy for them to survive - so they shrank almost to nothing.
Two, I think the onset of puberty just scared all the others off - they suddenly had other lumps and bumps to compete with and couldn't handle the pressure!
I have since had one or two threaten to appear on my foot and hand, as soon as even the slightest glimmer of something wart-like appears now I dig them out ASAP - not had one for years now, touch wood.