I think there are many reasons why people still buy bitcoin. one may be because people are more likely to increase the value of bitcoin so once they invest in it they can easily grow their investment and think that it is easier for them to live up to their lifestyle
People still buy Bitcoin because people are rational by which I mean to say that they know about the time to buy and the time to sell. They can see the future return in an asset if the prices are stable for some time. Besides, Bitcoin has so many other benefits to offer that are not offered by other coins and that is why people invest in Bitcoin. Long term investment gives more than enough.