If evolution were a fact, the whole universe would have filled with life-forms (just like a field becomes filled with weeds as the passes by) in view of the (virtually) infinite time that has already passed!
Not every place in the universe is hospitable or conducive to life. Might I add that you are made of the most common elements in the universe, with the exception of helium, because it is inert.
yet we were unable to prevent extinction of many species that have already happened and how are we going to prevent extinction that is now under way?
That's usually because we killed them directly or indirectly, and usually with our technology. There is a reason we don't have as many such large land mammals anymore.