Not without reason: Stardew Valley, which has been sold to millions of gamers, has been created using the free MonoGame engine. So ConcernedApe is giving back to the open source software which made his commercial success possible, like commercial parties should.
Gifts do not confer obligation. Copying deprives the original party of nothing. Absolutely nothing about free software requires or even implies any responsibility to “give back”. This idea that anyone making money with free software somehow owes the original authors anything (or “should” donate a portion of their profits) is ridiculous. If the authors wanted money for their software, they would have sold it instead o…
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He also needs that tool to stay alive for the future, even if not considering the past.
It's a bit better position for everyone.