Making software open source doesn't mean you can't make money from it. Depending on the details of what you build, who uses it, how you license it, etc., it may be harder to make money from it than if you made it proprietary. But that certainly isn't something you can just take as a given. You also can't take it as a given that the project would make money if it was closed source either. Maybe you made something nobody needs. Or they need it, but there are better alternatives out there (possibly some that are Open Source). Who's to say?
Somebody yesterday (maybe DannyBee, not sure) made a very insightful comment in saying that sometimes the value created by Open Source software is created exactly because it's Open Source.
Anyway, you can always charge for software even if the code is Open Source. You can stick it on the web and make it a SaaS app, or you can make the source available but charge to download binaries (ala JBoss back in the day), or you can make source and binaries freely available and sell subscriptions, etc. Aaah, wait, I know, you're asking "who would buy a subscription for something that's free to download?" Companies. Companies will, for things that are mission critical, because they typically need for their to be a contractual relationship (eg, somebody to sue) in place. Or you have a manager who needs to spend her budget or lose it, and she understands that you need to make a profit in order to stay alive and keep enhancing the software. Etc., etc, yadda, yadda, ad infinitum. My point is, it's not as simple as "Oh, I made this Open Source, so there's no way to profit from it".
The underlying issue they are trying to solve is that developers believe they should be able to extract some of the wealth they feel they created. In open source, that wealth is often only created because the software was free. Otherwise, people would have used something else that was free but worked well enough. Developers like to often argue this isn't true, but history shows it to be true basically always :) So saying you should be able to extract this wealth is probably wrong. Saying you should be able to get paid a reasonable amount of money is not.
Somebody yesterday (maybe DannyBee, not sure) made a very insightful comment in saying that sometimes the value created by Open Source software is created exactly because it's Open Source.
Anyway, you can always charge for software even if the code is Open Source. You can stick it on the web and make it a SaaS app, or you can make the source available but charge to download binaries (ala JBoss back in the day), or you can make source and binaries freely available and sell subscriptions, etc. Aaah, wait, I know, you're asking "who would buy a subscription for something that's free to download?" Companies. Companies will, for things that are mission critical, because they typically need for their to be a contractual relationship (eg, somebody to sue) in place. Or you have a manager who needs to spend her budget or lose it, and she understands that you need to make a profit in order to stay alive and keep enhancing the software. Etc., etc, yadda, yadda, ad infinitum. My point is, it's not as simple as "Oh, I made this Open Source, so there's no way to profit from it".