Spinning can occur in many variants, while there is only one way not to spin. Therefore the chances for spinning is much greater when the planets are created from aggregation of different matters.
Under some rare conditions the spinning has slowed down to zero (The Moon e.g.)

A day is the time it takes for a planet, moon etc to rotate on it's own axis. A year is the time it takes for it to pass around the sun.

On this basis, one of the planet's moons (I don't remember which) has a year that is shorter than it's days! It rotates that slowly.