a lot of people who buy bitcoin because maybe I think they can still benefit from bitcoin just imagine you make this thread in 2013 while now in 2018 you must regret for selling bitcoin too fast.
Some other basic reasons are also here, as people are entering into the market for their own desires of getting huge profits from here. They want to get benefited with the Bitcoin from all the sides to make their selves rich and people call them millionaire and billionaire tomorrow. So another reason is to make name is the society and in the world therefore the demand increases.