i think they keep investing bitcoin because they know in the future, bitcoin will increase higher and higher value so that they get a big profit when they trade it to someone.
This is the best time to buy bitcoins because of its low price, I don't know when it will rise again, but surely it will. For those who are buying bitcoins right now, just hold it guys and wait for it before the year ends, who knows, maybe what happened last year will happen again or it will skyrocket again even more, if that happens, that would be a huge success for us.