Remember the pendulum: a longer pendulum swings more slowly. The same logic applies to limbs and wings, which behave like pendulums built out of muscle and bone.

A short limb (or a short wing) is a "short pendulum" — it naturally wants to oscillate fast. A long limb is a "long pendulum" — it naturally wants to oscillate slowly.

This is why small animals move in a blur and large animals move almost in slow motion — not because of effort, but because of size itself.