The whole ufo/alien thing has stemmed from Hollywood, and the New Age beliefs. For some reason people have tried to tie Alien life in with the bible which is just... wrong.
The bible doesn't really address this issue, and why would it? Hollywood, and pagans made it up. The plainly states the only beings of intelligence that he has created are angels, humans, and animals.
*Keep in mind that Earth was created before any other planet, and star was created(Planets were likely created on the 4th day with the sun, and stars.)
*The bible talks about man's redemption. Never mentions the fate of other beings that are from other planets.
*When judgment day comes ALL will be destroyed, including other planets, sun, stars...
Now, since the bible tells us that the destruction of the universe is based on people here on Earth, then why would God create other life in the universe then destroy them and everything he has created based on our fall here on Earth? That doesn't seem fair.
As far as why would God only create Earth with life on it... well, God hasn't revealed all the answers to us. We do know the God made the sun, moon, and stars to provide light for us and for use to be able to distinguish time(months, days, years, seasons...) Planets also play a role in this as well.