1. The late buyers who were chasing it at 15,000 to 18,000 price zone and suffered losses when it collapsed to 10,000 level. Now that price is coming back to 12,000 - 13,000, some might be eagerly awaiting to unload some.
2. The spate of negative news circling round the media about how each country's central bankers are banning the bitcoin mania. This would impact and affect the late buyers who had missed out all the fun and see their neighbours or friends who had made the windfall to get in. They are thinking ; "What if another round of selling starts"? "Is there some truth in all these news I have been reading?" These hesitation or procrastination are translate to delayed demand that might otherwise help to prop up the price level.
As the can be huge within the day, be sure you know what you are doing, have a strategy, SL in place and manage your own position size well.
All the best !