Bitcoin's value is constantly increasing. Why is the price of bitcoin increasing over time?
It is because the buyers of bitcoin are increasing. The spread of bitcoin is continue and with the passage of time more and more people know about it and they invest their money in bitcoin so with that demand the price of bitcoin increase.
Well, that is a very reasonable reason because its only about the law of supply and demand therefore if demand is high so the price will increase. It is true that more and more people around the world who are investing bitcoin and that is a transparent reason of continuous rising of bitcoin price.