You loved the time when you were nine and made biscuits for a stall, sold them to people and turned a profit; it wasn't really the money, it was the excitement of seeing that people really liked what you'd done and were happy to prove it by giving up something unambiguously valuable.
Next time, you added different colored icing, and it was fascinating to see which colors people went for and which didn't appeal. You learned, and it made you confident.
You get a thrill out of guessing correctly what other people require, though it's not just guesswork, of course, it's because you're always on the lookout for little revealing signals that people don't even know they are sending.
You love profit because it is, in many ways, an achievement of psychology: the reward for correctly guessing the needs of others ahead of the competition.