In my opinion there are two main reason for selling. One of them which is quite happening is panic selling as most of you know. When bitcoin holder sees that prices are going down sharply, he or she get scare and start selling with the herd. Second reason is the need for cash.
Exactly the only reason I can think of panic selling and emergency needs. Why would I sell it for a bike when several months later I can buy a car with the same exact amount of bitcoin. Or maybe there is one other reason why people are selling bitcoin, because they are daytraders! Buy low sell high
This very moment bitcoin is in bad state compared to last year achievement. Impatient newbies will be surely sold all their bitcoin posession and later calling it a scam