Because if the thing I'm doing is, for instance, making artisan screwdrivers, I don't spend my whole day making money. I spend my whole day making screwdrivers. If I love making screwdrivers, then I love making screwdrivers.
Now that I have all these real nice screwdrivers lying around, I can sell them to other people who might want a really nice screwdriver. Not only did I get to do the thing I enjoyed doing: making screwdrivers, but I also made some money off of it. Some of that money can be used to cover cost of materials on the screwdriver I made, the rest of it can be used to enrich my personal life, or maybe grant me access to stronger tools to do the thing I enjoy doing.
Making something and selling something are two different tasks. I can love making things and still sell those things for a profit, and my love for making things can have absolutely nothing to do with the fact that I get money out of it. Where do you get the presumption that you can't possibly do something good that you like and still make money off of it?
