People use to hold bitcoins because the biycoin analyst says that its price will touch 10k $ mark in 2018. And in the current month people has witnessed that its price has jumped from around 4k to 6k. So that was a good jump in crypto market. So peiple beleive in its rise.
Bitcoins price is rapidly increasing now a day as every one can see. There are many people in the world who predicted that bitcoin will reach 10k $ in comming years and will become a international currency which is accepted all over the world. So due to this most of the people hold bitcoin now.