In the last decade I've hired about a dozen graphic design, media, and photography freelancers, and it's extremely difficult to build trust with a new hire without having prior experience with that person. What "trust" is to me is not the ability to make great things, but the inability to make bad things. The only way I can know that a photographer has a >98% success rate on projects is if I do 50 projects with them and only one is a catastrophic failure. If I hired one remote photographer for each job, I'd have to brief them for 1-3 days on the brand, my standards, my target audience, familiarity prior media created for the brand, etc. and they still will have a high chance of their work being unusable to me. Or I could just use my favorite photographer/designer for the job and not worry about training or the risk of their work being a miss. I suppose the same exact logic makes sense for aid agencies.