If it weren't for the open-source movement, most projects would never see the light of the day. I would never see myself working on my own products without the help of Github and its public repositories, for example.
In fact, the most important components of an app are often open-sourced, and some of the most cutting-edge technologies are only available as raw git repositories with very little literature: open-source is what drives modern innovation.
I could go as far as stating that open-source contribution is akin to charity. Even more valuable, sometimes. Brilliant people give their time and energy to build cathedrals that often go unnoticed. It takes tremendous efforts to manage a software project, let alone a whole community, and many open-source projects aren't monetized.
It's pretty rare to have companies build and maintain repositories from scratch, because there is no easy way to make a profit from it and engineers are expensive. It's a long-term investment. For some maintainers, it's a weekend or after-work thing, and it takes a whole other level of courage to do that.
Getting involved in open-source is the first thing I'll do if I ever make it to profitability. It's primordial for the advancement of humanity, and I would forever feel ashamed if I was somehow unable to give something back.