There’s a difference between helping others out and working an unpaid job for others. When you help someone it’s on your terms. You can always walk away if they ask you to do something you don’t want to do.
Normally if you have a job then you’re paid to do things you might otherwise not want to do. I like the example of an artist. If you’re an artist then maybe you’ll be happy to paint someone’s portrait for and even give it to them as a gift. However you’re unlikely to want to sit there all day creating character art for someone else’s video game project (a lot of meticulous, tedious, and/or uninteresting work).