I sort of understand the reasoning on why Arxiv prefers tex to pdf[1], even though I feel it's a bit much to make it mandatory to submit the original tex file if they detect a submitted pdf was produced from one. But I've never understood what the added value is in hosting the source publicly.
Though I have to admit, when I was still in academia, whenever I saw a beautiful figure or formatting in a preprint, I'd often try to take some inspiration from the source for my own work, occasionally learning a new neat trick or package.