I agree with you on some things :

Yes I have and still do Pirate some things (In My Case it's TV Shows)

Yes I Agree that its no different for someone to pirate a mod as it is to pirate a tv show or music.

However here is the problem; In the world of the internet everything is anonymous for the most part, a mod that replaces animations say could be made by one person, but then should another person come along and upload that to console without the credit of the original author, people will think that this new person made the mod; Then lets say someone else does the same thing;

Eventually it will be so hard to realise who made the original mod that it won't matter, and the original author who put the time and effort in won't get anything back, now by that I mean the sense of accomplishment or acknowledgement, in simpler terms by pirating mods you remove the psychological payback that people get from making said mods;

You also take away any attention that Mod author would of otherwise generated, which they may want for a number of reasons like the one I mentioned or another. An example is the dev of the Skyrim mod, Falskaar, who made his mod in the hopes of becoming a game dev, something that later happened; If someone had pirated his mod and not provided credit, how would anyone determine who is telling the truth barring something hidden in the actual mod.

Now onto why this is different; Firstly TV for example is made in the hopes of making money be it through ads or other sources, The people who work on TV they get paid for what they do, they receive something for the effort they put in, in a shorter time-span; When TV is pirated that hurts the network, which can then hurt the employees;

However at the same time the TV show cannot be listed as someone else's, and have the other network taking the money from the show, otherwise the offender would be sued for falsely claiming otherwise, so in that aspect the original author is protected on the information level, the harm to the employee's is also mitigated slightly as many people will still watch via TV networks, though the lost revenue still is an issue for the network.

The point is, the difference between the two is that a TV show that has been pirated still informs people as to its original author providing a psychological reinforcement to its creators but they also they get monetary reinforcement. If a mod is pirated, the mod author might not get either which means the dev will not feel appreciated, they won't be getting paid at the very least for the time they put in and this might mean they will go on to not make mods anymore and ultimately this will hurt the modding scene.