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 $1.
Most of the people buy it because of the hype and speculation in place. Which means if everything plays out right you would not have to wait 5years for it to hit 16k$ but less time. However that's why bitcoin is seen as an investment with high risk. Other people might buy it because they use it for other purposes rather than speculation. So you either buy bitcoin because you believe in it, you are using it in one way or because you like to gamble.