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.
In fact most of the people do not have any other option. Although bitcoin has a very good potential to increase its price and we already seen for so many times in past, People already have take good profit from bitcoin and still they are expecting that the price of bitcoin will continue increasing, and that is also a reason that they are holding their bitcoins.