There is no 'why' to any of it. If you want your life to have meaning then give it some - make an impression, leave a mark.
For us the most important question is 'how'. When we understand how something works (eg gravitation, nuclear fission/fusion etc) we can exploit that knowledge to manipulate our environment. This puts us in a better position to survive a random event - such as Planet Earth being hit by an asteroid - for which there is, equally, no rhyme or reason.
I am, of course, talking of an 'ideal world' situation here.