Those of us that value contributing where and when it makes sense to us.

For example, I have submitted a trivial patch to one of the tools in FreeBSD. And it is now part of a base install of FreeBSD, which means that when I install FreeBSD from official media, my patch is already included “free of charge” – that is, I don’t have to apply the patch myself on top of the official sources, nor to maintain a separate build of the tool in question. I benefit, and other users benefit.

Likewise I have some software on GitHub that I have released under the terms of the ISC license. Others may submit pull-requests, and if their patch is in line with my goals for the software, or if does not burden me overly much to maintain my software with those changes merged, I will merge the patches. The people that submitted the changes benefit and I benefit.

Meanwhile, sometimes I may want to modify a piece of software and not share the change. Being free to choose whether or not to share my changes benefits me. Likewise, me not forcing others to share their changes to software that I release under the terms of the ISC license has the potential to benefit other people.