For this discussion it's best to ignore material that didn't come up from Mr.Toriyama himself, since it's very likely that this tidbit is from him and other sources will not comply with this.
Know Planets:
Planet Earth
New Namek
Very Likely Planets:
The planet Vegeta, Nappa and Raditz were conquering before going to Earth.
Planet Yardrat
Freeza's Empire Center (Fair to assume they had a Planet as the Center of the Empire)
Galactic's Patrol Planet (Once again we should assume they have a Planet as their center of operations)
Possible Planets:
Monaka's Planet(Assuming he lives somewhere with enough population to be considered).
Metalman's Homeworld
Planet Zoon (Pocus Homeworld)
Planet of Darkness (Yakon's Homeworld)
Planet Sweets (Mentioned in the Manga)
Planet where Tarble and his wife live.
Main Causes
- Boo's cycles of destruction. This factor should be the most relevant for such little life.
- Beerus being a bad Hakaishin and destroying based on his humours.
- Freeza's rule who as we know destroyed Planet Vegeta and must have killed trillions or more of mortals.
- Kaioshin inexperience a consequence of Majin Boo's killing his fellow Gods. This might have result in him failing to create new planets and helping younger races to prosper.