My personal reason people are holding because i believe bitcoin is very good investment for long time future so people trust him bitcion holding long time money.
If we could just be as practical as we can be then, it is very simple, to make a lot of profit. Well imagine years ago this currency is almost second to none but now as you can see its value sky rocketed to the moon. And it obviously the current most expensive investment that a person could have.
For those people who hold on to this currency are definitely millionaires now.