It's actually a psycholergy thing. If something happens in the presence of many people, all of which could do something about it, it is unlikely that any of them will take action because they believe their share of issue is little to none. So they just kinda stand there slackjawed. Just observe what happens when a fire starts. Often, the fire could have been contained easily had anyone nearby done anything about it, but instead people stand there slackjawed until the fire grows huge and then they panic and trample each other and most of them die. That slackjawed herd CAN be motivated into action should somebody immediately begin shouting orders to people, though. People, being often sheeplike, react to any kind of decisiveness.
The same applies here: When you post something in a request section, if many people were capable of fulfilling the request, everyone's gonna think someone else will do it. So nothing is done. Requests sections only work when it is believed that only a small number of people are capable of filling the request.
Dear god, my sides are hurting.