I believe it's a result of Earth's equator not being perfectly circular, and the resulting irregularities in gravity causing satellites to drift toward one of two stable points at 75 degrees east longitude and 105 degrees west longitude.
It may be a big problem if a Sattelite Went out of control . There are innumeros Space derbis in the space. And every year we are launching Many sattelites. How much time can we control These Satelites And Space junks. Cannot Imagine . But Theres sollution- Using the Junk matterials of derbis can be resycled For the new one's