what makes you think that's what most people do? on the contrary, i think most people sell the bottom and/or buy the top. they get greedy when price is rising and don't want to sell. that's why the old warren buffet saying always applies. 
that is the logical move for anyone who is not a hardcore trader who cares only about making money. of course there is the buy high sell low situation but that doesn't mean people aren't going to spend 0.001-0.01BTC of what they have.
I myself would be willing to just use bitcoin to pay almost anywhere.