Putting money in a financial investment ultimately means lending it to other people so they can make stuff, and it's perfectly logical to compare it against a production investment where you make stuff on your own.

Of course, if all tomato growers closed shop and put their money in index funds, we wouldn't have tomatoes any more. But that would make the price of tomatoes shoot up and the return on index funds crash down, making tomatoes a better investment than index funds.