For many things, that's only true as a technicality. Having access to the source code of a complicated piece of software doesn't instantly make it easy, or even remotely feasible, to fix it yourself.

For example, back when I ran a Linux desktop and had problems with my video card or video settings, there wasn't a chance that I could fix it myself. The odds of me being able to do so were roughly equivalent to the odds of being able to fix a broken closed-source video driver by opening the binary up in a hex editor. Technically possible, yes, but not remotely feasible.