There are legal and financial reasons for this. You can't use a living (or recently deceased) person's likeness without their consent and without compensation; why pay someone for their likeness when you could select an older leader for free? Not to mention that recent events are not history (general rule of thumb: if it happened in the last two decades, it's journalism, not history). Then there's the fact that the more recent a person is the more likely they are to be controversial. There are very good practical reasons why the bulk of the leaders should be from the Renaissance or earlier; even as long ago as the 19th century many leaders remain deeply controversial.
One of my old history professors used to characterize many events and experiences as "Not history, but the stuff from which history can be made."
History comes from a Greek root word meaning "to learn by study" and basically, it is hard to study anything from the inside - if you lived through it, it is Experience which someone later can make History out of.
This is why I do not think that Contemporary Events, People, and Actions are a good basis for Civs, Uniques, or named Leaders in the game: we are too close to them to make a decent evaluation of their historical importance or meaning.
Besides, with 3 - 6000 years of historical Civs, events, Uniques and Leaders to choose from, depending on the last 50 - 75 years for them seems like a sad lack of application on our part . . .