I think to assume that most of Yuzuru's fans are also not fans of figure skating, or enjoy other skaters, is a bit unfair. It also doesn't take into consideration that a lot of top skaters have already withdrawn so the draw for Milan has already been waning even before he announced his withdrawal. I personally know several people who are his fans who still plan to attend, but I also know a couple of fans who are looking to sell their tickets and I hold nothing against it. Traveling to watch figure skating is expensive and often tiring. If one of the main reasons you planned to go see a competition is gone, and you have the possibility of getting back some of your investment back, there's nothing wrong with it - it's not like tickets were sold out to begin with and I'm sure many will try to sell their tickets discounted as I heard the original price was extremely high this season for Worlds and it deterred people from planning to go to begin with.
Yuzuru also gave very clear hints immediately after he won gold that he would likely miss Worlds due to the injury, but he probably had ideas of actually competing at Worlds if the prognosis of his injury allowed him to (there were news reports spotting him getting his medical check up just 2 days ago, so this likely sealed the deal and the news came out immediately after). Besides, many people already purchased tickets to Worlds well before the Olympics and well before he got injured so the timing of the withdrawal wouldn't have helped in their decision to buy a ticket.