Answer:
1. Size of Mars is smaller
2. Distance from Earth
3. Dust Storms
Step-by-step explanation:
The three main reasons that we can not see the features in detail are:
Mars is almost half in size than Earth and also at a minimum distance of 54.1 million km. At such a large distance with half of its size the details are not visible very prominently.
One more reason is the continuous dust storm over Mars which blocks our view of the surface of Mars.
But still when Mars is closest to us and has a clear weather we can spot the polar ice caps using a normal telescope on Earth.