You can also earn money when Bitcoin price goes down. In terms of margin trading, this is called short position.
For example, if the current price of Bitcoin is $600, and you expect that the price will fall, then you can get profit from selling borrowed Bitcoins for $600 now and buying them back later at a lower price.
You have $300 on balance and open a short position with 1:2 leverage for 1 BTC, which means that you pledge in $300 of your own money and borrow 1 BTC.
You close the position when price is $400, the 1 BTC you have borrowed is automatically returned, and your profit is 0.5 BTC minus fees.
This could be impossible without margin trading.