But that doesn't answer the question. If I buy shares in a business, I am helping that business to grow, and I am rewarded if it does. If I buy Bitcoin, nothing changes except that the price of Bitcoin goes up.

Basic economic rules are not designed but result of trade.

If you buy in the present what others want to own in the future, you create value for yourself as the price of the asset rises.

You can also understand Bitcoin as a business. Assuming it's a better form of money, it allows any agent of the system to better store or transfer money.

By owning Bitcoin you are assuming a risk, but also making the total value locked (TVL) bigger, through making the token less volatile. That helps. :-)

You are helping the world to transition to a better money, which will have tremendous positive effect on the society: https://www.youtube.com/watch?v=8zYg4E4zbPo