From wikipedia:
Contrary to popular conception, there is no evidence that societies relied only on barter before using money for trade.[73] Instead, non-monetary societies operated primarily along the principles of gift economics, and in more complex economies, on debt.[74][75][76] When barter occurred, it was usually between strangers or would-be enemies.[77]
it’s not even really a small community thing, it’s just about general culture and people’s ability to feel safe.
If you’re not lacking for anything then why wouldn’t you help others out?
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).