Most common reason could be that because it does fall crazy at times and this scares people. I do not know if I talked about this before but I believe that when you see it peak at 69k and then crash to 15k, you do panic when you see a fall. Same goes for what happened in the past, from 20k to 3k, or from 1.4k to 100 dollars. Every time there is a bear run the fall is huge and people just want to get out. Plus, there are traders out there, who want to get in and out constantly, every single day and that means they will sell. Combine these two types of people all together and you are going to get something a lot of fall.