Most of the times its a result of FOMO ( Fear of Missing Out ) this causes them to put all their savings into bitcoin. if they are confident that the prices will be around the same levels or lower or it will not get out of hand they make rational decisions.
i met a few people who think that bitcoin will reach 100k in a year or two and then it will be impossible to buy so why not buy when it is in reach. things like this make people do such things.