I just wonder if you want to earn in bitcoin investment then a smart investor would invest in while bitcoin is cheaper and not the current price.
Is there any reason we can think of why people love to invest in bitcoin while market price is high?
Being a smart investor doesn't necessarily mean that you only buy when prices are cheap. You can still be a smart investor if you invest in businesses or assets that you think will be worth a lot more in the future(assuming you've done the research),
regardless of current price.
To answer your question, it's pretty simple. People buy at current prices because they think it will be worth more in the future.