Because there’s a cost to using it on one thing instead of another.
And because the person who invests money has choices, and often chooses the choice that works best for them.
Most people would be happy with a hotel that generates a profit of a thousand dollars a day. But if the hotel cost $50,000,000 to build, you’re bust.
Time costs money too.
That’s not the same as saying “time is money,” which it isn’t. Time is magnificent, hard to stockpile and impossible to recover.
But it still costs. Which means that it’s worth considering whether something worthwhile comes back for your investment and your effort.