Human beings are strongly influenced by their surroundings. Science is the best way we have of learning more about the universe we live in, and to me the most important thing about any kind of science is that we gain new knowledge which changes the way we think and behave. The will to learn new facts about the universe, facts which no-one has ever known before, is the mainspring behind what I do every day, and I think that is true for most if not all scientists.
Since knowledge leads to power, science also allows us to shape and influence our environment, and as such is at the root of todays global society. Whether we can shape our environment intelligently is of course a critical question.
Finally, pushing the boundaries of knowledge in areas like particle physics requires us to push other boundaries - notably in technology (accelerators, cryogenics, computing) and also in human organisation and international collaboration. Making a worldwide collaboration of 2500 physicists deliver a one-off, dauntingly complex project like ATLAS at the LHC really does push that one! The long-term investment and policy making are also real challenges.
A few reasons there, but you might summarise them as “because science is what made us what we are today, and is our best chance for tomorrow!”.