Monetizing mods is hard, you will need to police the community to make sure assets are not stolen, handle QA and refunds, compatibility between mods, you also need to keep the community happy - you see with latest paid mods from Bethesda where people are asking questions like "why should I pay 5$ for a few armors and a weapon when a 15$ DLC had new teerain, new NPCs, quests, armors etc.