There are some people which thinks like it's written on thread's title but such relationship with bitcoin simply wasting of time because bitcoin is great cryptocurrency for trading which gives you opportunity to get good profit. Bitcoin is money, it's currency and it's exchangeable to any local currency so keeping bitcoins and not selling, I can't explain why someone will do this. Buy it, sell it and sometimes hold for higher profit, that will be good.
Different reasons for everyone as the price of bitcoin fluctuate and never be stable in the nearly future.
People who sell their bitcoin are make after profits from trading and convert into fiat money which so tempting to do, a general cycle of bitcoin environment.
Back to the case that Op mentioned, if there are a lot of merchants accepted bitcoin payment, a lot of people won't convert bitcoin into diat money and spend it directly instead. But, we know the price will increase, would you spend it or hold for another level of price?