as far as I know, most people buy bitcoin is to sell them, for another fiat, or for moving to another area.
expect day trader who do trading bitcoin is to make a profit that just like other forex or stock, why do you buy bitcoin, if you are not a crazy fans?>?
i buy them usually when their price is small to sell later for more, aka trading, and i think that lots of people buys bitcoin just for this reason, or to gamble them, to earn money from it
but now when steam accepts bitcoins i think that some people might buy them to pay for steam games, maybe even keep them for while to get more value from it