Actually bitcoin is like others coin so its price can be high and low. So if people see that the price of bitcoin is high so they can sell. They can save something for the future also. There is nothing as stupid decision.
I absolutely agree with you. How can selling bitcoin be a stupid decision. It will be stupid if you sell it when the value of bitcoin is still low. Of course, you can't earn much profits from that. Be sure to be wise in investing bitcoin to assure much profits.