The demographics have changed around the first- and second-generation malls enough that many of them are no longer viable. Since they're huge properties, they tend to rot slowly. They're finally dying. There's probably some fundamental challenges wrt online shopping, and preference for more "natural" environments, but there are plenty of malls that are doing very well, especially the more upscale ones.

Just because not every mall is succeeding, it doesn't mean the whole category is doomed. (Not that I actually like them, but enough people certainly do.)