Obviously, as the more people before me, they said that is the difference in the exchange rate over the time. But except this, after a while one can have a significant amount due to just not spending his coins. Clearly for many people it's a way to put their savings in a safe heaven, though the crypto currency volatility, but without the fear of the inflationary fiat money.
Yes I agree, to get the maximum benefit we have to be patient for a long time (more than 1 year), based on the price movement from 2013 until now the bitcoin price always rises.
The price does not always goes up but you can take advantage of this too and obtain even more bitcoin by being able to sell when the price is very high and buy when the price is very low that way you can get great profits without too much of an effort and in a relatively fast way