Fear of insecurity, fear of the unknown, i think thats why people tends to lament when btc prices fluctuate, these set of shivering investors are indecisive, they were probably tricked into investing in btc against their wish,thats why they tend to wave when prices drops and quickly wants to sell off instead of seeing that as an opportunity to stuck up more btc.
I think the expectation of the people that people have from bitcoin is the main cause that compel people to moan about the bitcoin price. In fact people were so much confident about the bitcoin price that they even invested their money in bitcoin when the bitcoin price was trading above 19000$, but unfortunately the bitcoin price dropped too much from that level.