It doesn't hold the platform back because if the hobbyist didn't scratch his own itch he was never going to spend 1000x as much development effort creating a Photoshop competitor or even yet join the effort to triage gnome bugs. We would almost certainly just be less their contribution for no benefit. This whole faulty analysis relies on treating open source developers as a fungible resource like employees of a firm that ought to be tasked with something different. It's not so.