You are completely right that they want to get a cut and it's bullshit.

But I don't see anything wrong with paid mods, where all of the money goes to the mod author (which this situation isn't). Some mods take months to develop and a massive amount of skill, and it's sensible to expect payment for it.

It's a false dichotomy between "corporations profiting" and "all mods need to be free". To me both situations are losing ones.