Because I need to pay my bills which do not accept Bitcoin, not at least here in Hong Kong (hoping it is different in the west).

And holding Bitcoin and selling it to pay Fiat means I eat the spread...(nobody will exchange both ways at the sport rate). Given the spread I have to tolerate, it makes no sense to hold Bitcoin for less than at least three years to be in the red, that too depends on the cycle timing. In other words, I can put into Bitcoin roughly what I do not need for a few years at least. Luckily, I have a decent job and have that luxury to think a few yeas ahead, but I understand many do not.

The right question!