I'd say it's because you consider the 'GREATNESS' of a discovery is correlated how well it answers a simple question that almost anyone can come up with. Evolution is a great answer to simple questions about life for anyone willing to accept it, but subatomic particle research just doesn't have immediate implications to most people.

Edit: Also, what are your thoughts on technology? While it isn't a theory or scientific discovery, personal computing has had a major impact on society in the last couple of decades.