For some of the more notable bloggers, because everyone knows they're on Team Apple. They aren't just people who have a lot of Apple products, they're people who have significantly bought into Apple's worldview and culture. Since tech punditry as a whole is very tribal, trashing the other teams regularly is par for the course, but trashing your own team is seen as a betrayal, an extraordinary event, a reaction to the company's own betrayal of the pundit's heightened trust. The latter is newsworthy, the former is not.
(While this mentality is strong in Apple-land, it certainly has its place among Google partisans as well, among others...)