You are absolutely right, that is not a .NET specific issue, it was just very little time between these big libraries going commercial. I think that there is a deeper issue here. Maintaining an open source project is hard work and is rarely compensated, I can even understand the motivation of the mantainers that decided to put their projects under a commercial license.
Businesses and developers profit from foss software, but the chances that anything, be it money or support via contributions, is given back are low. I don't think that it is desirable to go closed source to solve that issue, but I also don't have a good solution at hand.
Pretty sad to see. Although I have no significant proof to back my feelings, I sort of feel that the .NET ecosystem is still very corporate-minded and open source is not getting the love it deserves from the community. That is especially sad because modern C# and .NET are great tools for writing software.
Businesses and developers profit from foss software, but the chances that anything, be it money or support via contributions, is given back are low. I don't think that it is desirable to go closed source to solve that issue, but I also don't have a good solution at hand.