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.
Considering the fast growth of bitcoin price no wonder why people are holding bitcoin. If you will thoroughly figure it out , bitcoin has been all over the internet and many people especially in highly developed countries are using it as there leading currency. Having the patience and cleverness to hold it some more time will lead you to greater chance of being rich because its price will surely increase more than 50% of its current price.