1) people expect it to achieve greater value in the future
2) you might want to make it circulate so that it makes bitCoin an important coin, making it last forever
3) you might be from some other country and might want to by something from accross the sea ... instead of buyin dollars, you can buy bit coins (that's what i am gonna do)
~~~~~~~~~~~~~~~~~~In that case when I sell them Bitcoin, I got their money, I will have to transfer to USD my self?
4) this might be your business, to buy bitcoins to sell them to other people who need/want them (for any reason)