Patent applications like these, especially knowing that it's Apple making them, are usually meant for preventing the competition from offering a better product.

Apple itself has little incentive to actually use any better keyboards as long as nobody else is doing that, so by filing a patent on as many means of making an "ingress resistant" keyboard as possible they're able to stall their competitors. Even if the application doesn't go through, it'll still hang in the limbo of back-and-forth revisions for a couple years, and meanwhile nobody else can do anything lest they end up infringing and wasting their effort.