Question

Why is the motion of satellites around their planets considered an acceleration motion

Answer 1

this is because they have fixed time and distance

Answer 2

Motion of satellites around planets is uniform circular motion.
And object moving with uniform circular motion is accelerated motion.

Explanation:
When a particle moves with a constant speed in a circular path it's motion is said to be uniform circular motion .
In such a motion , speed is uniform but direction changes at each point. Due to change in direction of motion, the velocity of particle is not uniform HENCE the motion is accelerated.