Different people have different preferences. Just like how some people prefer to use cash when dealing, some prefer debit card, some credit card and etc. Each method have their advantages and disadvantages, but people still use them. Same argument for bitcoins.
They're still buying bitcoin because they believe it will rise again and it is only temporary the status of bitcoin price right now. They only take advantage to buy bitcoin in a lower price and hold the coin until the price high. Or they have different reasons to but it, it based on their plan or strategies.