I think the main reason to invest in bitcoin is the same as to invest in any other assets - make capital. Bitcoin is a volatile currency, thereby many people hope to gain a lot from trading. Another purpose of investing in Bitcoin is that people believe it will cost much more in the future, because the amount of coins is constant and can’t be more than 21 million. Also, some investors prefer to diversify their investment portfolio and in this case Bitcoin looks like a worth idea to put some money in.