If people buy Bitcoin at $8,000, they will get 100% profit only when Bitcoin reaches $16,000. If it takes 5 years to reach $16,000, people will earn more money from Gold and Silver than from Bitcoin. Silver is giving 20% to 35% profit in one year.
Mining cost of one Bitcoin is $5,000 or more. When Bitcoin was $400 or $800 it was understandable because people had to just spend $400 or $800 to get one Bitcoin and $1,200 is super high profits when Bitcoin started from $1.
I think it is because many people still wanted to earn from investing in bitcoins. It is also an opportunity to easily earn money and especially during times when bitcoin price starts to go up after it has fallen down low. And people also want to just hold longer their bitcoins then wait for it will go up again though it would take so much time.
There are some reasons why some people are buying bitcoin its because they wan to divert their saving into an investment so that while keeping their money in safe place they can still earn once the market is playing very well.