For me it's a combination of a few of these. We are still very early in the adoption phase where I live it's very hard to find vendors that accept BTC. in addition to that the upside for BTC price has the potential to be massive so I want to get as much as I can before it take takes off (not that I have that much). Also whilst fiat is still everywhere there's also Gresham's law in play. Why would I use money that is going up in value and hold onto money that is going down in value.