Why couldn't it be? Because they're working on an existing platform? Because they're adding paid content to an already paid product? That's like saying RUF workers shouldn't be ever paid because they work on already produced Porsches. Modders should charge whatever they want, I think that pressuring modders into releasing free work 100%of the time is detrimental to the quality of the mods we could have in the end. No one is forcing no one to buy bad mods if they don't want. On an other tangent, I see people expecting dev quality out of every single paid mod, that's just entitlement. It's not because you're paying a mere 4€ for a mod that the creator becomes compelled to your every desires, beginner modders spend as much time as the better ones, and will still need margin to improve, that's how it work in every creative fields.