Being Such A Small Planet How and Why Does Pluto Have So Many Moons?

The old theory is that Pluto is an escaped moon of Neptune, actually. Pluto shares a 2:3 orbital resonance with Neptune. It's likely that other Kuiper Belt Objects were captured into that resonance and so that is why they're orbiting one another.

By the way, I was going to add more thunder but the 2nd answer stole it.

"An astronomical body's Hill sphere is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit that lies within the planet's Hill sphere."

The size of a planet's Hill sphere depends on the planet's mass and also its distance from the Sun. Though Pluto is small, it's so far from the Sun that its Hill sphere is larger than Earth's. That means there's lots of space for Pluto to have moons in.

Yes it is a bit of a surprise.

Perhaps in 2015 when New Horizons arrives we will get some answers.

If Pluto had collided with Uranus, we wouldn't have Pluto where it is now. And besides Pluto is way too small to have affected a huge planet.