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.
that's true. i remember first getting into bitcoin to play poker on sealswithclubs back in 2012. i forgot about it, then when i saw the april 2013 bubble, i immediately bought amazon gcs with all my coins. then the price kept going up and i got hooked to the markets....
also and mostly i am talking based on BitPay stats. for example this chart from 2 years ago was the best thing i can show you. it maps number of processed transactions by BitPay (the bars) versus the price (the line). it shows an increase number of them during the ATH of 2013 and a big drop after price came down and then slow growth afterwards
good point. however, we should also note that total network transactions were strongly trending upwards through the april 2013 bubble, then sharply dropped from may-june 2013. we see an even more pronounced increase in total network activity from august-december 2017, during the last bubble: https://www.blockchain.com/charts/n-transactions?timespan=all&daysAverageString=7
this tells me there is a correlation between price bubbles and network activity---it's not just that more people are spending via bitpay. if there is an increase an network activity, we should expect some ~proportionate increase in bitpay activity as well.