Contributions to non-copyleft OSS licenses _are_ actual contributions to the open source community as a whole.
There's nothing preventing your GPL'd project from being used to make a commercial product that you are not a part of either. You're talking about enforcing perpetual conditions on the future of the product/license for your free labor. This is the reason why projects like MAME have contributor agreements now.
Even if through some process the license changes in the future, your contributions were still to an open source license and that version of the code will remain open forever.
I haven't seen anyone discouraged from contributing to OSS-licensed projects that are not GPL unless they are an extreme ideologue. I myself generally prefer to license my work with something like MIT or Apache (read: the ISC license, generally) and that choice is absolutely fine.