Traditionally, contributors to free software and open source, especially the more prolific ones, are often good programmers. This has made its way into the collective consciousness in a way that affects hiring, e.g. by considering open source contributions as a positive signal.
People who want to be software developers hear or read about this and want to replicate it, so they are looking for somewhere to contribute. Hence initiatives like in TFA, and GSoC etc.
What they ignore or just don't see is that those traditional contributors to open source largely self-selected by having some issue that they wanted to solve and then just fixing it. They come to the projects with their own issues, which may overlap with issues of others out of coincidence. The difference in motivation and internal drive is significant.
Of course it's still nice when people genuinely want to contribute to make the world a better place, but I'm skeptical about the support burden that these non-traditional contributors often put on project maintainers, because they tend to need more guidance on average and have less intrinsic understanding of the problem space and relevant use cases. Some projects grow structures to support it and manage just fine, but some don't and I think that also needs to be accepted.