The reason to make a new one is because there is meant to be an ecosystem.
Coins are not there for new people to find and mine, coins are there to trade for one another and support bitcoin.
NEW coins made (by you) are for you and your friends to mine, or for your school to mine, or for your team to mine, or for your WoW clan to mine, or whatever.
Then those coins are to be traded for other coins and used to support Bitcoin.
why not using bitcoin directly?
Because it is extremely hard to mine, and expensive to purchase.
Pretend I am 14 and I come to this thread. Not only am I 14, but the only reason I have a computer is because there was a company running a program that gives kids in the ghetto Tablets with a bunch of books and internet access.
Now...
How can I (the 14 year old with only a tablet) EVER hope to get in to Bitcoin? I can't.
BUT
If a friend of mine makes a NEW coin, and tells me about it, then someone makes an app for Droid mining. Now I (the 14 year old) have a chance of actually breaking in to the Bitcoin market.
You also can text your friend who have some btc, and buy a little bit for real money and now you are in, why not do so?