I don't think that's obvious. There aren't necessarily easily interchangeable contacts available for more than that, and for many people $500 in under ten days

I don't think that's obvious. There aren't necessarily easily interchangeable contacts available for more than that, and for many people $500 in under ten days is more than they would earn in their job. Students for example could easily be qualified to do this, perhaps be on a break and have time, and would otherwise be earning nothing. Not to mention the resume padding and connection building opportunities.