Valve takes 25% of the cut on any mod. The rest of the price tag for a mod will be decided by the developer company itself, in Bethesda's case it is 50% if I am not mistaken. So the community for Skyrim only gets 25% of the pay, if even that, and only if the mod in question surpasses one hundred dollars in total sales. The difference between this and the games / mods [member="Anja Aj'Rou"] listed is that those three mods have been made as standalone games with everything they need to function. The current system allows, if not downright forces people to pay for mediocre cosmetic that were otherwise free on the Nexus. Valve has also stated that if a mod is free, it can get incorporated in the mod / mod compilation of someone else to be sold for their profit, while the original creators get squat.
This will be as bad, if not worse, than the numerous micro-transactions and DLC that plague major titles, only that this time around it puts the modding community at risk of dieing because nobody wants to have their work stolen and sold by others for a quick buck while getting minimal to zero credit for their work. This will also put Valve at risk of legal suits because if someone get's a get-rich-quick scheme of making a texture mod that allows you to play as a Final Fantasy character or someone from a Blizzard game, Valve will be directly responsible for it because they are trying to monetize their intellectual property.
This is nothing but Valve trying to squeeze more money out of their platform while indirectly, unknowingly, and / or callously killing off the modding community as we know it. Hell, modding was never even about the money, it was a way to get familiarized with a games engine and, if you did a good enough job, score an internship at a company or have the possibility to start your own due to your knowledge. It was a hobby, something you did out of passion for the game, not something that allows scam artists to make a quick buck of fools and be transformed into another Early Acess parade of crap.