I agree with your point of view but that's just one of the reasons people invest in Bitcoin. Almost everyone makes money to live, and investing in 2017 is a wise decision when the value of bitcoin goes up by the end of the year and then in 2018 the market is not very good. People see investing in Bitcoin as a passion.
But people make a mistake by investing in 2017 because in 2018, bitcoin price is down and now it's down too deep without any highly increase. Some of them are desperate for the price can increase again, but the other still believe and sure that bitcoin price will increase in the future. Maybe they need to take a deep breath and accepting the losses they made in the last year so it could make them keep survive.