I think this statement is painting the world a bit too black and white. Of course I can only speak for myself, but having just watched the following video about the A380 by FBW:
I feel that many open source developers (and for the sake of simplicity I am including freeware developers here as well) feel the same like I do. And that is we are intrinsically motivated to do something great, to the extend that we want, without any financial pressure or âsteering committeesâ, deadlines and what not (yes, Iâd claim that most open source developers are professional software engineers deeply embedded in âtraditional software development cyclesâ, and hence drive their open source projects forward in their free time).
And there follows that most (all?) open source developers not only write their software for themselves, no, they want to publish it, make it available to the community, get recognition and feedback, and fix reported issues as quickly as possible - or at least respond with a âqualified feedbackâ asap (again considering the time constraints, see âfree timeâ).
But to first add to your argument: yes, the A320NX actually was in the marketplace (for free)! And yet it was pulled by the dev team. As far as I know several developers were not happy with the license conditions from the marketplace, but I donât know the details.
So yes, some developers certainly feel the way you just described.
On the other hand most open source developers are not against companies making âbig moneyâ. Remember my claim: most open source developers are actually employed as well as professional (as in âmaking moneyâ) software engineers.
And making money is generally a good thing! This ensures that the product will receive more funding. There might be this romantic myth of every open source developer being Robin Hood, fighting the âbig corporationsâ and giving away the goods (here: the software) for free to the people.
Well, I donât think thatâs true - for sure not for me. Yes, there is a certain group of open source developers that really have an âopen vs closedâ source politic, and are fiercely following their ethos. But letâs not go down that routeâŠ
So bringing home my point here: most (all) open source developers want their fruits be brought to the market. And the larger their audience, the better. And they are not âanti-capitalisticâ. So if there was an easy (easier) way to bring in freeware/open source add-ons into the MSFS marketplace I am sure many developers would consider this.
Sure, you would have to abide to certain legal agreements, assert that all your assets really belong to you, you have to deal with âlegaleseâ in some way, you might become liable in some way⊠all that âcorporate stuffâ that you are actually trying to avoid in the first place 
And of course you need to adhere to the technical standards of the marketplace: installation folder structure, provide all correct config files, âno executablesâ and all that (which might even limit you in what you intend to develop).
But then again this would open up a much larger market of people that might not know about places like flightsim.to, not to mention âhow to unzip and move the add-on into the Community folderâ (âwhat folder?!â).
And all open source developers want their product be exposed to the community as much as possible. Because that is the reward they are after: knowing that people are actually using - and liking - their add-on, or simply put: to get recognition from the community 