Most people just see a mistake, correct it, imagine and forget about the project? Or are they constantly involved in the product creation process?
I definitely fall into the first category (focusing on a long-term project is not my business), but there are many people who are part of the second. Without them, we would not have a lot of viable ecosystem of free software. A significant portion of these people are paid to write and maintain open source software, but there are still many lovers who do this just for fun. In fact, most of the people I know who get paid to work with open source software will still contribute if they have to do it for free (I would do that). Deposits will be less frequent.
How can you participate in open source projects?
When I was a student, I played with the internal structures of various free open source programs (including gdb, OpenSSH, arping, some IRC clients, Snort, various Perl modules, some specific packages for Debian, ...) and fixed some errors , as well as the implementation of several functions. Nothing great from the SLOC point of view, and some of these contributions were rejected, but it was still fun and interesting.
I became a co-founder of the Free Software Users Group, which has been operating for over 4 years. In meetings, I sometimes give technical presentations about free software. We also try to regularly attend external events, invited by LUG / FSUG.
I also often buy t-shirts, sweaters and fluff from projects that I like to give them some kind of financial contribution.
Now I am engaged in technical support in an open source company, and therefore I report errors and regularly fix corrections. And they actually pay me for it. Why choose between contributing to Open Source and real work when you can do both?