Why does bitcoin is such a big currency when converted in real money ?
There are many factors that affects the price of bitcoin but the most important one is the law of supply and demand. Unlike your local fiat system which has almost unlimited supply Bitcoin only has a maximum of 21 million pieces once everything is mined and this amount can't be increased but rather keeps on decreasing due to people forgetting their wallet passwords and people dying without passing their password to their kin.
Bitcoin's price will keep on increasing as time goes by specially when more and more people becomes aware of it and sees that it has uses. But I think the reason why it's price is going high right now is because of people's greed.