There is only so much Bitcoin that will ever exist, every day less and less bitcoins are being “mined”. Unarguably, bitcoin is very popular, which creates more demand for it. The supply however, is limited. That's were the basic principles of Supply and Demand comes in. You want a bitcoin, Everyone wants a bitcoin, but its limited. Which means that in order for you to get that bitcoin you need to pay more than me and the other person that wants a Bitcoin. There is more demand than available supply. Also, the legalization of other countries in using bitcoin might also affect its  value. Also the prediction of experts also affects its current value. And I think it will continue to increase.