Except that in Skyrim there are extremely few mods that would be of that caliber. A few of course, things that are the size of DLC. There are a few mods with new large regions, some are good, some are extremely buggy, none really I would call "great". Even for DLCs I wait until the price drops to $5 anyway. So for one of these large&good mods, the price point would be $1-2. Yet that's what most people were trying to charge for junk and fluff; $0.99 for a retextured sword is stupidly expensive, and yet some people were actually defending this as an appropriate price.
I have 71 mods I've used for Skyrim (none with nudity). Do you really think I should pay $1 or even $0.50 for every single one of them? Added up as a total they do not equal a single game. If they charged, I'd do without the vast majority of them. Ie, windmills have turning blades in a mod, it's nice to have but I'd be stupid to pay for that. Many of them I tried and then after a few minutes uninstalled again as they were nothing like what I expected. Most were the work of big teams of volunteers. Pay for the unofficial patches? Most players would never do that and it would cause the game to get an even worse reputation for buggyness without them. A large chunk of mods were people just trying things out or making something for their own personal use, and just uploading it to Nexus to see if anyone else wanted it. I could do without all of them except the unofficial patches and the SKUI. Charge for mods and the players using mods and the number of mods they try out would shrink by at least a couple orders of magnitude.
What about open source? Should I be paying money for each Linux patch or feature? How would it survive if everyone who wasn't paid took their toys and went home? Even if they charged a small fee the majority of people would never even try it out.
After the paid option went away, some modders said that they could no longer justify the time and expense for modding and were giving up on it. Yet if Valve/Bethesda had never added this option or hinted about it I know that these people would have still been at it, volunteering and doing it for free. That's because they did not do their early modding work with the promise and hope of being paid later; they did it all even though as far as they knew they would never be paid. But have some paid mods for one weekend and take it away, they just packed up and went home like something was stolen from them.
I've paid for Mozilla when that was an option, and people called me stupid at the time for doing it. I've paid for Linux distributions. So my point is not that I want free stuff and want to be a freeloader.